In Orberg’s LLPSI he has the Magister asking the pupil (after the pupil has written a word badly: ‘hoculos’ for ‘oculos’):
Quid significat 'hoculos?
Now I think that ‘Quid’ here is the neuter nominative singular interrogative pronoun. Is that right? The interrogative pronoun is used to stand in for a missing thing or person in a sentence, e.g. ‘What is the matter?’ or, as in this case, 'What does ‘hoculos’ mean? or ‘What is the meaning of ‘hoculos’?’ - where the meaning is not to be ‘found’ in the sentence…
If it were an interrogative adjective then the thing it refers to would have to be in the sentence so the Magister would have asked: ‘Quod significationem habet ‘hoculos’ putas?’
(not sure about construction of my examples here…)
you are indeed on the right track re quid - the neuter nominative singular interrogative pronoun. It just asks ‘what?’ or ‘Which?’, or sometimes ‘Why?’.
Re your other example, it would be a little different. If the teacher asks “what do you think that ‘hoculos’ means?”, you would still use ‘quid’: Quid putas hoculos significare?
Alternatively, if you want to ask ‘what meaning does [the word] “hoculos” have’, you could not use the neuter ‘quod’, because ‘significatio’ is female. I think you would also use ‘-ne’ to indicate it’s a question, not a statement: 'Quamne significationem habet “hoculos”?
“-ne” indicates a yes-or-no question, and is not used with the interrogative pronoun. It does what we do in English sometimes by putting the verb first, sometimes by intonation alone: “Verbumne “hoculos” est?”, Is “hoculos” a word?, or “Hoculos” is a word?.
Sometimes the surest way to formulate a question correctly in Latin is to answer it in something of the manner of an unhelpful robot, by simply replacing the interrogative pronoun or adjective with a demonstrative one. The answer to the question “what meaning do you think “hoculos” has?” is: “You think that “hoculos” has this meaning.”
This helps you (or at least me) see that it should be an acc + inf. construction (“You think that…”), and that “this meaning” is the object of “has”, and so should be accusative.
The robot’s answer, in Latin, could be: ““Hoculos” hanc significationem habere putas.” To make the question, we need only put the interrogative adjective back in: “Quam significationem “hoculos” habere putas?”