"When do we arrive?"
Translation:Wann kommen wir an?
This is a separable verb: ankommen (to arrive), which is formed from the verb kommen (to come) and the separable prefix an. When you conjugate separable verbs, the separable prefix breaks off from the main verb and is put to the end (in simple sentences like this anyway...I could explain how this changes with conjunctions and different verb tenses if you wish, but I don't want to overload you with information).
So, with separable verbs, you conjugate the main verb as normal and put the prefix at the end, e.g. Wir kommen an (we arrive), or some other examples:
- fernsehen (to watch TV) -> Ich sehe fern
- einladen (to invite) -> Wir laden ihn ein
- mitkommen (to come with) -> Kommst du mit?
Note: Some separable prefixes have a pretty consistent meaning, like mit (which on its own means with, so when you combine it with a verb, it adds the sense of "with", "coming with", "going with", "singing with"), while other prefixes have less clear meanings on their own or may have more idiomatic meanings.
WH questions start with the WH word or phrase, as in English.
So wann? comes first.
Then comes the verb -- or at least the stem, minus the separable prefix. So from ankommen, the wir form is ankommen, or kommen ... an.
kommen comes next.
Then comes the subject: wir.
The separable prefix goes to the end of the sentence. Since there are no more words in the sentence, it comes next: an.
Wann kommen wir an?