If you wrote "I wish an answer" then it is not a grammatically correct sentence.
If you wrote "I wish FOR an answer" then I believe it should have been accepted. Whilst it is less commonly used, it has a similar meaning to "I would like an answer". In many cases, it is closer to "I DEMAND an answer".
Like the former replier said, "ønsker" means to wish or want something very bad, and "vil" is just "want". In this case you could actually write "Jeg vil have et svar" and it would be correct, but that's not always the case. Think of the difference as:
Ønsker = would like/wish Vil = want! (fist banging table)