"How to [...]?" and "Where to [...]?" Questions that are not questions. Is this defensible?

The sentences would be properly phrased in prose as follows:

How do I punctuate a list of questions?
Where do I put the periods when using a parenthetical sentence?

[D]o i can be alternatively phrased as does one, if formality or third-person point of view is required.

The examples you gave would be more suited to the title of a how-to guide, such as:

How to Punctuate a List of Questions

In other words, the article that follows would instruct one on punctuating a list of questions. This form is not for a question, but instead for a title, and thus should not be punctuated at all.

I have always thought of how to do x? as short for something like how [is one] to do x?, where the question mark is necessary.

I'll give a shot at answering my own question.

The obvious correct alternatives are not entirely satisfying.

How does one punctuate a list of questions?

This comes across as too formal for many people.

How do I punctuate a list of questions?

This is too personal, perhaps selfish sounding.

How do you punctuate a list of questions?

This sounds like it's asking for opinions rather than established usage. (On this site you'd get a warning about a subjective question.)

How to Punctuate a List of Questions

This sounds like an introduction to a guide.

So the problem is probably that using one has become too formal and nothing has reliably taken its place.

Perhaps a better alternative would be to rephrase the question:

How should a list of questions be punctuated?

Is this practice defensible?

Obviously, since people have defended it. ;)

Perhaps the real question is down to whether the defense is justified.

For my part, I'll search a post for '?' and if the first hit is ..

Know someone who can answer?

(N.B. Directly quoted from StackOverflow, which itself seems to fall into the same 'not a sentence' area.)

.. I will scan the post for a goal then directly, put 'How to' in front of it, and a '?' at the end. I deliberately choose not to alter the goal in any other way, in some sense as a way to indicate:

Look how easy it can be to turn a goal into a question!

OK - not for the 'grammar conscious', but then, there are not too many of them who make comment in any group other than this one.

English is an evolving language. This is a very good example for change. If "How to [goal]?" is not a valid question then it is English that should change.

Am I being unreasonable?

IMO (for whatever little it is worth) yes.

The question mark, by itself, is enough to make any statement a question. For example:

The sky is blue?

By mere word-choice, the sentence appears to be a simple statement about the color of the sky. However, the question mark adds clear disbelief and uncertainty on the part of the speaker, and the sentence above can be read with an implied introductory phrase:

(Is it true that) the sky is blue?

While I personally wouldn't use either of the examples you provided, their uses seem like attempts to depersonalize and shorten the questions being asked. Consider:

• How to punctuate a list of questions?
• How (should I) punctuate a list of questions?
• (What is the right way) to punctuate a list of questions?

Note that the expanded variants are both several words longer, and introduce unnecessary conditions to the basic question. (Specifically, the second implies a question of style rather than correctness, and the third prespposes the existance of the wrong way to accomplish the task.)

Such language forms are not questions at all; they should never be ended with an interrogation point. That, however, is easier said than proved.

Let's take the short and common "how to speak" and a few others of that sort. We find first that it is a form that is the core of numerous titles in which there is never an interrogation point.

• How to Speak How to Listen
• How to speak well under all ordinary conditions
• Mastery of Speech: How to speak under trying conditions
• How to Argue: Powerfully, Persuasively, Positively
• How to speak well in public
• Communicate: How to Speak Well in Public and in Private!
• How to speak correctly and pleasingly
• How to speak on public occasions
• How to speak in daily business life
• How to speak in private life and in public places

Other instances without link
1 How to Be a Good Mom — How to use words correctly — How to find material for talking and speaking — How to Sell Like a Star Salesman — How to Give a Fashion Show — How to be a Good Role Model for Your Child
2 What to Wear: A Style Handbook — What to Wear to a Seduction — What to wear for snowmobiling — Why Women Wear What They Wear — What Not to Wear: For Every Occasion — What Happens to Your Body When You Cycle — EXCEPTIONS: 4 times "What to Wear?" as a title
I believe those 4 exceptions and possibly a few others of that sort are errors, the reason being that there is no possibility of a principle dictating that zero complement should imply the necessity of an interrogation point; in my opinion a subjective principle is at work so as to induce the writer into perceiving a legitimacy that has no foundation.
3 When to Speak Up and When To Shut Up — When to Say Yes and Make More Friends — When to Kill — When to Use What Research Design — When To Walk — When to Fight and When to Forgive — When to Bypass Back Surgery — How and When to Be Your Own Lawyer — What To Say And When To Shut Up — When to Do House Cleaning Jobs —

The list of such titles goes on and on, the same pattern being preserved (no interrogation point).

One should become convinced that all these forms have no particularity that should make them proper for titles only: they can all be fitted in plain affirmative sentences. First of all, it is clear that they can all have the functions of subject and direct object in a sentence; the reader will soon be convinced of that by trying a few on the model provided below and as well by a little research in the books.

• How to speak well under all ordinary conditions is not a subject-matter taught in elementary schools.

This means that all these forms have the status of nominal phrase; they are, for all grammatical purposes, virtual nouns. The grammatical nature of the form precludes therefore all uses of an interrogation point, except of course in an elliptical context.

• maps? forests? course? snow? … (no meaning attached)

• — The wheel is warped! — The wheel? (Is the wheel warped?)

• Clean Air? (This will be rare; title of a book in which the ellipsis is of a very puzzling nature, very "undefined", but proper to stimulate the imagination: "You Said 'Clean Air'?", "Is Clean Air your Concern?", …)

As I understand it, you are asking for a reliable published source that could confirm, one way or the other, whether a 'How to ...' or a 'Where to ...' clause takes a question mark at the end.

Your first example from this site was originally a 'How to ...?' form, but it has since been edited to a standard question; your second example stands at the time of posting this answer.

These patterns are described in the Longman Student Grammar of Spoken and Written English by Douglas Biber, Susan Conrad, and Geoffrey Leech (Harlow: Pearson Education, 2002) p 324, section 10.10.1. (henceforward, LSG)

The section deals with 'wh-complement clauses' (which include how) in post-predicate position. The two examples they give with 'where' and 'how' are:

1. 'You must also understand how to check their accuracy at recognised stages' (Academic)
2. 'I would tell [them] where to go' (Conversational).

I would argue that the examples you give all fit a pattern of initial implication, and the use of the question mark at the end of them would depend on the nature of the implied words.

For instance, an implied 'Do you know ...' would justify the question mark; an implied 'Let me tell you ...' would justify a full stop/period.

What's interesting is the semantic analysis on p 325 of the LSG which looks at 'wh-complement clauses' in two domains: cognitive and speech. In Table 10.2, the authors show that the verb 'to know' is by far the most common verb used to govern 'wh-complement clauses' in the cognitive group. It occurs in all four domains they look at. In speech, the most common verb used to govern 'wh-complement clauses' is 'to tell' although this doesn't occur in academic texts.

Your second example could easily be read either as 'Can you tell me where to put the periods when using a parenthetical sentence?' or as 'Do you know ...?' And on StackExchange, this would trump the cognitive domain interpretation of 'Let me tell you where to put the periods ...'.

From IMDb {Harry Potter and the Philosopher's / Sorcerer's Stone; Rowling}

PHILLIPS: (As Sorting Hat) "Hmm, difficult. VERY difficult. Plenty of courage, I see. Not a bad mind, either. There's talent, oh yes. And a thirst to prove yourself. But where to put you?"

DANIEL RADCLIFFE: (As Harry Potter) "Not Slytherin. Not Slytherin."

Usage trumps prescriptivist rules. And it's a win-win situation when the rule-breaking examples are perfectly understandable, stylishly free-flowing, and gripping. This dialogue doesn't contain a single complete sentence (except arguably There's talent[, ...]). It's a string of fragments, one an interrogative in deleted form. But let the person who would improve upon it first gain the following the books and the films have amassed.

In many cases, it is silly to argue against the acceptability of sentence fragments. Though equally, in many cases standard sentence structure would be a great improvement.

Just to set the record straight here (it is not likely to be crooked elsewhere), the declarative form of question has long been used in both speech and writing, and continues so. Use of the question mark (eroteme, note of interrogation) as terminal punctuation for declarative questions is standard, common, and, as far as it goes, 'correct'. Both of these examples,

How to punctuate a list of questions?
Where to put the periods when using a parenthetical sentence?

are converted into declarative questions by use of the mark; without the mark (or other suitable context), they would not be questions.

Prescriptive grammarians now and in the past endorse, and use, questions terminated with question marks in declarative (as opposed to interrogative) form. Goold Brown, for instance, who invented and adopted the term 'eroteme' (deriving it from 'erotesis') to refer to question marks, explicitly endorses its use for declarative questions in his 1851 (revised 1857) The Grammar of English Grammars. The work contains a number of examples of his own and others' use.

Obs. 4 — A question is sometimes put in the form of a mere declaration; its interrogative character depending solely on the eroteme, and the tone, or inflection of voice, adopted in the utterance: as, "I suppose, Sir, you are his apothecary?" — Swift: Burgh's Speaker, p. 85. "I hope, you have, upon no account, promoted sternutation by hellebore?" — Id. ib. "This priest has no pride in him?" — Singer's Shak., Henry VIII, ii, 2.

p. 769, bottom.

No less a contemporary prescriptive grammarian than Lynne Truss, in the seminal popular grammar Eats, Shoots & Leaves (2004), certainly uses declarative questions, repeatedly, even if she does not explicitly endorse their use (she might; I can't tell without actually reading her corpus):

Readers are obliged to get used to the idea from an early age that "Double or single?" is a question not applicable only to beds, tennis and cream. (p. 171, middle)

In the old days, we used to ask the following question a lot: "One word? Two words? Hyphenated?" (p.189, bottom)

Descriptive grammarians, of course, have no shortage of declarative questions in speech and writing to draw from, as is evident in, for example, a book chapter in Abduction, belief and context in dialogue: studies in computational pragmatics (2000, pp. 311-26) by R.J. Beun titled "Context and Form: Declarative or Interrogative, that is the Question":

You said Monday?

The italicized utterance by I is an example of a question in D-form [declarative form]. Here, the use of the declarative as a question is accentuated by the question mark.