The phrase "look for" usually needs to have something after it:

I'm looking for a gift for my husband.

But in questions, that part comes earlier:

What are you looking for?

There's an old rule that some English teachers might try to enforce, which says that you shouldn't end a sentence with a preposition like "for". According to this rule, you're supposed to say or write:

For what are you looking?

But this is really strange and old-fashioned. You can use it in extremely formal writing, or maybe as a joke.