Learn Hardcore German: Ich weiß nicht, wann der Zug ankommt. - I don’t know when the train arrives.

In German, wann introduces an indirect question (“when”). wenn is used for conditional clauses (“if”) or repeated events (“whenever”). Since you’re asking “when the train arrives”, you need wann.

Why is there a comma before wann?

Subordinate clauses in German (including indirect questions) are always separated by a comma. Here, wann der Zug ankommt is a subordinate clause introduced by the question word wann.

Why does ankommt come at the end of the clause?

German subordinate clauses follow the verb-final rule: the conjugated verb (kommt) goes to the very end. You’ll see this with most conjunctions and question words that introduce subordinate clauses.

What kind of clause is wann der Zug ankommt?

It’s an indirect question (a dependent interrogative clause). It functions as the direct object of weiß (“I don’t know when the train arrives”).

Why do we say Ich weiß nicht instead of Ich kenne nicht?

wissen is used for facts, information, or knowledge of when something happens. kennen is used for familiarity with people, places, or things. Since you’re talking about knowing a fact (“when”), you use wissen.

Is ankommt related to a separable verb?

Yes. The base verb is ankommen (to arrive). In main clauses you would separate it (“Der Zug kommt an”), but in subordinate clauses the prefix an stays attached and the entire verb ankommt moves to the end.

Why is der Zug in the nominative case?

der Zug is the subject of the subordinate clause: it’s the one doing the arriving. Subjects in German take the nominative case.

Could I use a different word instead of Zug?

You could use Bahn to refer more broadly to train services or the railway system, but if you mean a specific train, Zug is the most precise word. For example: Ich weiß nicht, wann die Bahn ankommt sounds more like “I don’t know when the train service arrives.”