The error here is not in Russian, but in the construction of the English interrogative sentence. *Is he* a typical reversion in the construction of the interrogative sentence.

As for the sentence in Russian, it makes no difference. *Он наш официант / Он наш официант?* are both grammatically correct, and in Russian it is not necessary to rearrange the words.

But if you want to suffer and show off your knowledge of Russian, here are the options for constructing a question:

• Наш ли это официант?

• Не это ли наш официант?

Yeah, you got it wrong. There is a question mark, so your answer should be «Is he….» not «he is.»