How to include a question in a declarative sentence?

I am assuming the intended meaning is that the question is "how do I specify {the identity of the thing, for which I am paying}" (rather than "how do I specify {what I am giving as payment}").

Neither of the options presented reads as correct English to me. The "For what I am paying" or "For what am I paying" object clauses are both awkwardly constructed, and it seems to me that they were arranged this way purely to avoid ending them in "for".

Use of 'to specify'

The second possibility is that it's a mistaken use of "for" with the verb to specify. Specify is a transitive verb - it takes an object - so there is no need to use "for" to indicate what is being specified:

• (correct) I specify the size, and they send it.
• (incorrect) I specify for the size, and they send it.

Proposed Answer:

The way that I would word this is as follows:

• ... how do I specify what I am paying for?

Despite the repeated claims to the contrary, it is perfectly acceptable for an English sentence to end in a "preposition", and in this example it is the most natural construction. It is also totally acceptable to use this in a formal context.

Whatever you do, please don't tie your sentence in a knot just to avoid ending with "for".

• (don't write this!) ... how do I specify that, for which I am paying?

1. I know that this is the website but, how do I specify for what I am paying?

2. I know that this is the website but, how do I specify for " what am I paying? " ?

The difference is simple. One contains a question (the direct speech) within a question, and the other does not.

However, I think 2) is incorrect and causes problems as @SAH said, the direct speech should be in quotation marks to differentiate from the indirect speech in 1) and the direct speech in 2). Because there is no quotation marks it is difficult to ascertain when the direct speech starts, whether it be from specify for (2a) or specify (2b)

2a.

I know that this is the website but, how do I specify for " what am I paying " ?

2b.

I know that this is the website but, how do I specify " for what am I paying " ?

I think you were right to go with 1), instead of 2), as it is more clearer and causes less confusion.

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_{* There are two options in English: (1) "Indirect speech": [ I know that this is the website, but how do I specify for what I am paying? ] (Note the comma.) (2) "Direct speech": [ I know that this is the website, but how do I specify: "For what am I paying?" ] (Note that "direct speech" must always have quotation marks around the reported speech.) – SAH Nov 13 '18 at 3:50}