You can't, you have to say: 'What does 'apple' mean'?
The reason is:
If you want to form a question or negate a statement, you have to use 'to do' together with the verb, e.g. to eat, to live, to consider .... (The only exception is 'to be'.)
Examples:
Where do you live?
What does he eat for breakfast?
He doesn't eat bread.
They don't love their children.
Exception: Where is he? ('to do' not necessary)
I suppose English people 'want' their real verb to be after the subject - even in questions- , so they put a form of 'to do' before the subject.
In your sentence 'apple' is the subject; 'what' is not the subject.
I hope that has helped you a bit and not confused you.