That must be the end of the first part of the performance. What a) happens b) is happening now?
P.S.: The correct answer is a) i.e.: What a) happens now. Why it's not Present Continuous we have the moment of speach now?
This example taken from Michael Vince's bookIt's the whole text (only a sentence)/ Taken from the exercise.

Question

That must be the end of the first part of the performance. What a) happens b) is happening now?
 P.S.: The correct answer is a) i.e.: What a) happens now. Why it's not Present Continuous we have the moment of speach now?
This example taken from Michael Vince's bookIt's the whole text (only a sentence)/ Taken from the exercise.

Answer

What happens next?
What happens now?

When describing a schedule we often use the present simple. Think about that for a minute.

If you describe a movie to a friend then you use the present simple. It's a rule in English.

Answer

Either could be correct depending on the context.

What happens now? (What happens next?) - This refers to the performance.  Simple present to describe scheduled future events or, in the case of a play, opera, etc., it could be the historic present tense for narration.

What is happening now?  - This could refer to what is happening in the theater itself, not on stage.  What is the audience doing?  Are the people staying in their seats or going to the bar for drinks?  Perhaps they are just standing up to stretch a bit.

Answer

I just tried to answer the question, but I'd like more of the text if you could type it up.

Answer

What happens now?
Nothing is happening, he is asking what will happen next.

It can /almost/ be replaced with next.