There are a few options here:
- When is the end of the world?
- When the end of the world happens?
- When is the end of the world going?
- When does the end of the world happen?
Any wrong options here? Maybe you have had some other variant?
closed as not constructive by Kris, kiamlaluno, MετάEd, FumbleFingers, tchrist Dec 28 '12 at 6:09
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This is grammatically and idiomatically fine. It's standard English. Another way of saying it is:
are both ungrammatical.
is a special kind of question. It implies a blasé attitude, sounds ironic, and suggests as much interest as "When does the shoe store close?" It's not a normal way of asking this question. But it's perfect for asking someone who believes that the apocalypse will occur today, for example, when it's going to happen. It's mockery.