case of “Bus” in “Wissen sie, wann der Bus kommt?”

Question

I know that

der Bus = the bus

and in the question

Wissen sie, wann der Bus kommt?

I would have thought that seeing the verb "kommen" is being used, the article of the noun "Bus" would be "den" i.e. in the accusative.

The idea I had was:

Wissen sie, wann den Bus kommt?

Why is the initial question in the nominative and not in the accusative?

Answer 1

That is because in sentences as

Wann kommt der Bus? or Der Bus kommt wann?

Gleich kommt der Bus. or Der Bus kommt gleich.

the item der Bus is the subject. It's the thing that performs the action of kommen. It's not performed on the bus, but the bus does it itself. So, the verb kommen has no objects. Wann and gleich are adverbials of time.

Same for your example. The different word order is because it's a subordinate clause but still, der Bus is the subject in that clause.