Ni atendos ĉe la stacidomo ĝis la trajno alvenos.

Because in Esperanto, if both actions are in the future, both verbs are normally marked as future.

So:

• Ni atendos = we will wait
• la trajno alvenos = the train will arrive

This is different from English, which often uses the present after until, as in until the train arrives. Esperanto usually does not copy that English pattern. A future event is typically shown with -os.

So ĝis la trajno alvenos is the normal way to say until the train arrives.

Ĉe usually means at, by, or near a place.

So ĉe la stacidomo means at the station.

Why not en?

• ĉe la stacidomo = at the station, in the area of the station, by it
• en la stacidomo = inside the station building

If you just mean the general location where you are waiting, ĉe is often the better choice.

Stacidomo is a compound word:

• stacio = station
• domo = house, building

Together, stacidomo literally suggests something like station building.

In actual use, it often means railway station or the station building itself, depending on context.

This is very normal Esperanto word-building: roots are combined to make a more specific word.

La is the definite article, meaning the.

So:

• la stacidomo = the station
• la trajno = the train

This suggests that the speaker and listener are talking about a specific station and a specific train, or at least ones understood from context.

A useful thing to remember:

• Esperanto has one definite article: la
• It does not have an indefinite article like a or an

So:

• trajno can mean a train
• la trajno means the train

Because neither word is a direct object here.

• la stacidomo comes after the preposition ĉe, so it does not need -n
• la trajno is the subject of alvenos, so it also does not need -n

The accusative -n is mainly used for direct objects, for example:

• Ni atendos la trajnon = We will wait for the train

In your sentence, la trajno is not the thing being directly acted on by alvenos. It is the thing doing the arriving.

Yes. Ĝis can be used with:

• a noun or phrase: ĝis morgaŭ = until tomorrow
• a full clause: ĝis la trajno alvenos = until the train arrives

So in this sentence, ĝis is introducing a subordinate clause.

That is completely normal Esperanto.

Because ĝis by itself already means until and can introduce this kind of clause.

So:

• ĝis la trajno alvenos = until the train arrives

Adding kiam is usually unnecessary here.

Ĝis kiam is more commonly used in questions, such as:

• Ĝis kiam vi restos? = Until when will you stay?

So in a sentence like yours, plain ĝis is the standard choice.

Yes.

• veni = to come
• alveni = to arrive

So alvenos is the future form of alveni:

• alvenos = will arrive

You can think of alveni as come to a destination.

That is why Esperanto uses alveni where English often uses arrive.

In Esperanto, atendi can mean both:

• to wait
• to wait for

So Esperanto does not need a separate word like English for in this meaning.

You can say:

• Ni atendos = We will wait
• Ni atendos la trajnon = We will wait for the train

In your sentence, the object is not directly stated, because the next part already makes the situation clear:

• ĝis la trajno alvenos

So the sense is naturally understood.

Yes. Esperanto word order is fairly flexible.

Your sentence has a very neutral order:

• Ni atendos ĉe la stacidomo ĝis la trajno alvenos.

But other orders are possible, for example:

• Ĉe la stacidomo ni atendos ĝis la trajno alvenos.

That said, the original version is the most straightforward and natural for a learner to follow.

No. The ending -os only shows tense, not person.

So atendos by itself could mean:

• I will wait
• you will wait
• he will wait
• she will wait
• we will wait
• they will wait

Because of that, Esperanto usually states the subject pronoun unless it is already completely clear from context.

So ni is needed here to show that the subject is we.

Usually, yes.

Using la suggests a train that is known, expected, or understood from context. For example:

• the train we are waiting for
• the train that is scheduled to come
• the train already mentioned in the conversation

If you said just trajno, it would sound less definite, more like a train or some train.

So la trajno is the natural choice when both speaker and listener know which train is meant.