Mi ne scias, kio estas en via sako.

Because kio is the subject of the clause kio estas en via sako.

In Esperanto, -n marks the direct object. But here, kio is not an object; it is the thing that is in the bag.

A helpful way to test it is to look at the verb:

• kio estas en via sako = what is in your bag

The thing being asked about is the thing doing the “being,” so it is the subject.

You would use kion only if what were the direct object, for example:

• Mi ne scias, kion vi portas en via sako.
  = I don’t know what you are carrying in your bag.

There, kion is the object of portas.

Because this is an indirect question, not a plain that-clause.

Esperanto uses words like kio, kiu, kie, kiam, kial, kiel to introduce indirect questions:

• Mi ne scias, kio estas en via sako.
  = I don’t know what is in your bag.

Compare that with a ke clause:

• Mi scias, ke ĝi estas en via sako.
  = I know that it is in your bag.

So:

• kio = introduces an indirect question: what ...?
• ke = introduces a statement: that ...

Yes, it is basically the same structure.

In Esperanto, kio estas en via sako is very straightforward:

• kio = what
• estas = is
• en via sako = in your bag

So it follows normal Esperanto clause structure. The verb estas comes after the subject kio.

This is one of the nice things about Esperanto: the sentence is very direct and does not require special question word order beyond using the question word itself.

Kio means what and introduces an indirect question.

The full sentence has two parts:

1. Mi ne scias = I do not know
2. kio estas en via sako = what is in your bag

So kio starts the subordinate clause and asks about the identity of the thing in the bag.

You can compare:

• Direct question: Kio estas en via sako?
• Indirect question: Mi ne scias, kio estas en via sako.

Same basic meaning in the second part; the only difference is that in the full sentence it is embedded after Mi ne scias.

Because kio estas en via sako is a subordinate clause, and Esperanto normally separates subordinate clauses with a comma.

So:

• Mi ne scias, kio estas en via sako.

That comma is standard and very common in Esperanto writing.

You may sometimes see styles that are a bit looser in informal contexts, but using the comma is the normal and recommended choice.

Because the phrase means in your bag, not into your bag, and there is no direct object here.

Let’s break it down:

• via sako = your bag
• en via sako = in your bag

After the preposition en, you normally use no -n when talking about location.

So:

• en via sako = in your bag
• en vian sakon = into your bag

That second one would suggest motion into the bag.

Also, sako is not the direct object of the sentence, so it does not get -n for that reason either.

Yes, but it would mean something different.

Esperanto can use -n after a preposition to show direction toward something. So:

• en via sako = in your bag
• en vian sakon = into your bag

Examples:

• La mono estas en via sako.
  = The money is in your bag.
• Mi metas la monon en vian sakon.
  = I put the money into your bag.

In your original sentence, the meaning is location, so en via sako is correct.

Because scii means to know a fact / to know information, while koni means to know a person, place, or thing through familiarity.

Here the speaker does not know a piece of information:

• Mi ne scias, kio estas en via sako.
  = I don’t know what is in your bag.

That is exactly the job of scii.

Compare:

• Mi konas vian fraton.
  = I know your brother.
• Mi scias lian nomon.
  = I know his name.

English uses know for both ideas, but Esperanto usually distinguishes them.

You may see that in very casual writing, but the standard form is:

• Mi ne scias, kio estas en via sako.

Esperanto generally uses a comma before subordinate clauses, especially when they are introduced by words like ke, ĉar, se, or indirect-question words like kio.

So for learners, it is best to include the comma.

Yes, in most contexts en via sako simply means in your bag or inside your bag.

The preposition en means in or inside. It does not usually add any special nuance beyond location within something.

So:

• kio estas en via sako
  can naturally correspond to
• what is in your bag
• what is inside your bag

depending on the context and translation style.

Yes. Kio does not itself mark number.

So the sentence could mean:

• I don’t know what thing is in your bag.
• I don’t know what things are in your bag.

However, because the verb is estas, which is the same for singular and plural, the Esperanto sentence does not force the distinction.

If you wanted to be more explicitly plural, you might rephrase:

• Mi ne scias, kiuj aferoj estas en via sako.
  = I don’t know which things are in your bag.

But your original sentence is perfectly natural and common.

You could expand the sentence, but kio by itself is already the natural choice here.

For example:

• Mi ne scias, kio estas en via sako.
  = I don’t know what is in your bag.

That is clean and idiomatic.

Adding extra words like tie would usually change the meaning or sound unnecessary unless you really want to emphasize location in a different way.

So for this sentence, the original version is the best normal form.

Via is a possessive adjective, meaning your.

It modifies sako:

• via sako = your bag

Like other Esperanto adjectives, possessives can agree with the noun in number and accusative case when needed:

• via sako = your bag
• viaj sakoj = your bags
• vian sakon = your bag (as direct object / with direction in some contexts)
• viajn sakojn = your bags (as direct objects)

In your sentence, no extra ending is needed because sako is simply part of the prepositional phrase en via sako.

Yes. That is just the contracted English version of the same meaning.

• Mi ne scias, kio estas en via sako.
• I don’t know what is in your bag.
• I don’t know what’s in your bag.

All of those are good translations. The Esperanto sentence itself is neutral and works well in either formal or informal English translation.

It is an indirect question.

The direct question would be:

• Kio estas en via sako?
  = What is in your bag?

The indirect version is embedded inside another sentence:

• Mi ne scias, kio estas en via sako.
  = I don’t know what is in your bag.

This is a very common pattern in Esperanto, just as in English.