Wann kommst du aus Berlin zurück?

Because zurückkommen is a separable verb.

• The full verb is zurückkommen = to come back / to return
• In a main clause, the conjugated part goes to position 2:
  • Du kommst ... zurück.
• The prefix zurück separates and moves to the end.

So:

• Wann kommst du aus Berlin zurück?

But in the infinitive, it stays together:

• Ich will aus Berlin zurückkommen.

In German main clauses, the conjugated verb usually comes in second position.

Here, Wann is the first element, so the verb must come next:

• Wann = position 1
• kommst = position 2
• du = after the verb

That is why German says:

• Wann kommst du ...?

and not:

• Wann du kommst ...?

The version with du kommst would be used in a subordinate clause, for example:

• Ich weiß nicht, wann du aus Berlin zurückkommst.

Aus Berlin means from Berlin in the sense of coming out of / away from Berlin as a place.

• aus is commonly used with cities, countries, and enclosed places
• It answers the question where from?

Examples:

• aus Berlin = from Berlin
• aus Deutschland = from Germany
• aus dem Haus = out of the house

So in this sentence, aus Berlin zurückkommen means to come back from Berlin.

German usually uses aus with:

• cities
• countries
• buildings
• enclosed spaces

So Berlin normally takes aus:

• aus Berlin

Von is more common for:

• people: von meiner Freundin
• places seen more as points rather than enclosed places: vom Bahnhof, von der Arbeit
• possession or origin in other contexts

A learner-friendly rule is:

• from a city/country/building → usually aus
• from a person / from an event / from a general location → often von

So Wann kommst du von Berlin zurück? would usually sound wrong or at least nonstandard in normal usage.

Aus takes the dative case.

That means the noun after aus must be in dative.

Examples:

• aus der Stadt
• aus dem Haus
• aus einem Hotel

In this sentence, it is:

• aus Berlin

You do not see a special ending here because Berlin is a proper noun without an article. But grammatically, it is still governed by the dative after aus.

Yes. Du is the informal singular word for you.

So this sentence is addressed to:

• one person
• in an informal situation

The formal version would be:

• Wann kommen Sie aus Berlin zurück?

Changes:

• du → Sie
• kommst → kommen

Even though Sie refers to one person here, it takes the plural verb form.

Sometimes learners confuse zurück and wieder, but they are not the same.

• zurückkommen = to come back / return
• wiederkommen = to come again / come back again

In many situations, both can be translated as come back, but zurückkommen strongly emphasizes returning to a previous place.

So here, zurückkommen is the natural choice:

• Wann kommst du aus Berlin zurück?

Wiederkommen would sound different in meaning, more like coming again rather than specifically returning from Berlin.

Wann is a question word meaning when, so it naturally comes first in a direct question.

German question words often start the sentence:

• Wann kommst du zurück?
• Wo wohnst du?
• Warum lernst du Deutsch?

Once Wann is placed first, the conjugated verb must stay in second position:

• Wann kommst du ...?

It is much more natural to say:

• Wann kommst du aus Berlin zurück?

German usually keeps the separable prefix zurück at the end, and the phrase aus Berlin fits naturally before it.

So:

• Wann kommst du aus Berlin zurück? = natural
• Wann kommst du zurück aus Berlin? = possible in very unusual contexts, but generally awkward

For learners, the best pattern to remember is:

• Wann kommst du [place/source] zurück?

The dictionary form is kommen.

Here is the conjugation of kommen in the present tense:

• ich komme
• du kommst
• er/sie/es kommt
• wir kommen
• ihr kommt
• sie/Sie kommen

In the sentence, kommst is the du-form of kommen, used as part of the separable verb zurückkommen.

Yes, it is in the present tense:

• kommst

But German often uses the present tense to talk about the future when the time is clear from context.

Because the sentence asks when, it naturally refers to a future return:

• Wann kommst du aus Berlin zurück? = When are you coming back from Berlin?

This is very common in German and works much like English:

• When are you coming back?

So you do not need a special future tense here.

In a subordinate clause, the verb goes to the end, and the separable verb becomes whole again.

Direct question:

• Wann kommst du aus Berlin zurück?

Subordinate clause:

• Ich weiß nicht, wann du aus Berlin zurückkommst.

Notice the difference:

• main clause: kommst ... zurück
• subordinate clause: zurückkommst

That is a very common pattern with separable verbs in German.