I think is safe to ask "where is the restaurant?" or, in a polite way, "would you tell me where the restaurant is?".
The first question is the basic "question-Formation rule".
The second one, you have the verb at the end of the sentence, because you moved the rest of it to the front of the sentence by the "question-formation rule" with the "would you tell me".
Plus, the first question express the idea "the location of the restaurant".
The second one, express the idea of "would you tell me".