Mi ne scias, ĉu ni fritu fungojn kun herboj aŭ ne.

Here ĉu introduces an indirect yes/no question. In English, that is usually expressed with whether.

So:

• Mi ne scias = I don't know
• ĉu ni fritu fungojn kun herboj aŭ ne = whether we should fry mushrooms with herbs or not

The same word ĉu is also used to ask a direct yes/no question, but here it is embedded inside a larger sentence.

Fritu has the -u ending, which is the volitive form in Esperanto.

This form is used for ideas like:

• command
• request
• suggestion
• proposal
• what should be done

With ni, it often has the sense of:

• let us fry
• shall we fry
• we should fry

So ĉu ni fritu... means something like whether we should fry... or whether to fry...

Why not the others?

• fritas = are frying / fry as a fact
• friti = infinitive, to fry
• fritos = will fry as a future fact

This sentence is about a decision or proposal, so -u fits best.

Literally, ni fritu is the volitive form with ni:

• let us fry
• shall we fry
• we should fry

In a main sentence, Ni fritu fungojn could mean Let's fry mushrooms.

Inside this sentence, it becomes part of an indirect question:

• Mi ne scias, ĉu ni fritu...
  = I don't know whether we should fry...

So it is not exactly a command here; it expresses an undecided course of action.

It could, but it would mean something different.

• ĉu ni fritu = whether we should fry / whether to fry
• ĉu ni fritos = whether we will fry

So:

• -u = undecided proposal, recommendation, or plan under consideration
• -os = future event as a fact

In your sentence, the speaker seems unsure about what should be done, not merely unsure about what will happen. That is why fritu is more natural.

Because fungojn is the direct object of fritu.

The action fry is done to the mushrooms, so Esperanto uses the accusative -n:

• singular: fungo
• plural: fungoj
• plural accusative: fungojn

So friti fungojn = to fry mushrooms

Because kun is a preposition, and after a normal preposition Esperanto usually does not use the accusative.

So:

• kun herboj = with herbs

The -n is not needed here, because herboj is not the direct object of the verb. It is part of a prepositional phrase.

Compare:

• friti fungojn = fry mushrooms
• kun herboj = with herbs

Aŭ ne means or not.

So the clause:

• ĉu ni fritu fungojn kun herboj aŭ ne

means:

• whether we should fry mushrooms with herbs or not

This is very natural in Esperanto, just as in English. It makes the yes/no alternative completely explicit.

The sentence would still be grammatical without it:

• Mi ne scias, ĉu ni fritu fungojn kun herboj.

That would still mean I don't know whether we should fry mushrooms with herbs, but aŭ ne adds emphasis and completeness.

No. This is a very common point of confusion.

• ĉu = whether / introduces a yes-no question
• se = if in the conditional sense

So here you need ĉu, because the speaker does not know whether something should be done.

Correct:

• Mi ne scias, ĉu ni fritu fungojn.
  = I don't know whether we should fry mushrooms.

Conditional se would be used in sentences like:

• Se ni fritos fungojn, ni bezonos oleon.
  = If we fry mushrooms, we will need oil.

Because ĉu ni fritu fungojn kun herboj aŭ ne is a subordinate clause, and Esperanto commonly separates such clauses with a comma.

So:

• Mi ne scias, ĉu...

This is standard punctuation in Esperanto. It is especially common before clause-introducing words like ĉu, ke, kiam, se, and so on.

By itself, kun herboj simply means with herbs, and context decides the exact nuance.

It could suggest:

• fried using herbs as seasoning
• fried together with herbs
• served with herbs

In ordinary usage, this is usually clear enough from the situation. If someone wanted to be more precise, they could rephrase it, but your sentence is completely normal.

Yes, it is natural and idiomatic.

A learner might find ĉu ni fritu... unusual at first, because English often uses whether we should fry... or whether to fry..., while Esperanto expresses that idea neatly with ĉu plus the -u form.

So the sentence is a good example of normal Esperanto grammar:

• Mi ne scias = main clause
• ĉu = introduces indirect yes/no question
• ni fritu = proposed action under consideration
• fungojn = direct object
• kun herboj = prepositional phrase
• aŭ ne = or not