Ili demandas, ĉu uzi diapozitivon aŭ ne.

Yes. Demandi in Esperanto means to ask.

So Ili demandas = They ask.

This is a common false friend for English speakers. If you want to demand, Esperanto more often uses words like postuli.

Ĉu introduces a yes/no question, including an indirect yes/no question.

Here it means something like whether:

• Ili demandas, ĉu uzi diapozitivon aŭ ne.
• They ask whether to use a slide or not.

So ĉu does not mean who, what, or why. It signals that the issue is a yes/no choice.

Because ĉu is used for whether / if in the sense of an indirect question, while se is used for if in the sense of a condition.

Compare:

• Mi ne scias, ĉu li venos. = I do not know whether he will come.
• Se li venos, mi ĝojos. = If he comes, I will be glad.

In your sentence, the meaning is not conditional. It is an indirect question, so ĉu is correct.

Because the sentence is talking about the question whether to use something, not stating a full separate clause like whether they use or whether they should use.

So:

• uzi = to use
• ĉu uzi = whether to use

This is very natural in Esperanto, just as English can say whether to use.

If you used a finite verb, the meaning would shift a little:

• ĉu ili uzas... = whether they are using / use...
• ĉu ili uzu... = whether they should use...

But ĉu uzi... leaves the subject unspoken and focuses on the action itself.

The subject of uzi is not explicitly stated. Esperanto can do this when the context makes it clear enough, just like English can say whether to use it without naming the person every time.

So the sentence does not grammatically say exactly who will use the slide. That has to come from context.

Depending on context, it could mean:

• whether they should use it
• whether we should use it
• whether one should use it

If you want to make the subject explicit, you can:

• Ili demandas, ĉu ili uzu diapozitivon.
• Ili demandas, ĉu oni uzu diapozitivon.

Because it is the direct object of uzi.

In Esperanto, direct objects usually take the accusative ending -n.

• diapozitivo = a slide
• uzi diapozitivon = to use a slide

So the -n shows what is being used.

The base form is diapozitivo.

You can break diapozitivon down like this:

• diapozitiv- = word root
• -o = noun ending
• -n = accusative ending

So:

• diapozitivo = slide
• diapozitivon = slide, as a direct object

Because the sentence refers to a slide in the singular, or possibly a slide as a general option.

If the meaning were clearly plural, you would use:

• diapozitivojn = slides

So:

• ĉu uzi diapozitivon = whether to use a slide
• ĉu uzi diapozitivojn = whether to use slides

Which one is best depends on the context and the intended meaning.

Aŭ ne means or not.

So:

• ĉu uzi diapozitivon aŭ ne = whether to use a slide or not

It makes the two possibilities very explicit:

• use it
• do not use it

Often ĉu by itself already implies this kind of uncertainty, so in some contexts aŭ ne could be omitted. But adding aŭ ne is perfectly natural and can make the choice feel clearer or more emphatic.

Because ĉu uzi diapozitivon aŭ ne is a subordinate clause attached to the main clause Ili demandas.

Esperanto commonly uses a comma to separate the main clause from a following subordinate clause:

• Ili demandas, ĉu...
• Mi ne scias, ĉu...
• Ŝi diris, ke...

So the comma helps show the structure of the sentence.

Yes. That is a good structural match.

A very literal breakdown is:

• Ili = they
• demandas = ask
• ĉu = whether
• uzi = to use
• diapozitivon = a slide
• aŭ ne = or not

So, word for word, it is close to:

They ask whether to use a slide or not.

In more natural English, the exact phrasing may vary depending on context, but the Esperanto structure is straightforward once you recognize ĉu and the infinitive uzi.