If you are asking a group of people if they would like to drink coffee, you would say "Who wants coffee?". If you asked this question, and a few people said, "No, thanks! I don't want coffee", then you could say "Who does want coffee?". You would put emphasis on "does" in this case since you already know who does NOT want coffee and now would like to know who DOES want coffee.

What is a G translation anyway? "Who wants coffee ?" = Who wants to have coffee = Which one of you wants a coffee? "Who does want coffee"?> Who does XXX > "Who does HE ..think he is /want to serve him?"