How to use a slash to describe two options, one of which is made up of two or more words?

There is an ambiguity in using the "/". It may connect the alternative forms of your information as a handbook (which, for example, might be paper) and as a knowledge base (which might be digital).

If this is the case, I suggest not using "/". It may be easily replaced by "handbook or knowledge base" or (even better, with no ambiguity) by "knowledge base or handbook"

Or does "/" merely connect the names of your information, being one thing that you describe with either of two names (for example, your handbook is only published online and you also describe it as your online knowledge base)?

In this case why use two names for the same thing? Better to use one name and not confuse the reader.

You can rely on the reader to interpret it correctly. "Knowledge base" is a common term. "Handbook base" makes no sense.

I think it's fine to leave it as "handbook/knowledge base." The odds of misunderstanding are very low.

All the possibilities you envisage are bound to be ambiguous for at least some of the readers, although the last solution of using spaces appears rather good.

There is the alternative of using a hyphen: handbook/knowledge-base; hopefully the readers would make the difference with "handbook-/knowledge-base".

Note: hyphens are used freely enough in English and they tend to be used increasingly.

Increasingly I find knowledgebase used as a single word..

Google's definition panel (apparently powered by renowned dictionary press Oxford Languages) proposes it as an alternative to the spaced version, even if Google itself asks you "did you mean knowledge base?", and one only has to hit google books for the phrase to see it's been used in print without a space for a very long time.

1. I have struggled with this for long and continue to struggle especially when I think that it could be mis-understood.

2. So, I use hyphens when necessary and skip them when I think that the term/usage is known to the reader or if it can be reasonably expected of the reader to have knowledge of such a term.

3. I definitely use hyphen when I think that the word/s following the last word after the last slash might be used with the word preceding each slash.