I think it is part of a yes-no question, where "có" is the yes part. Translations oft cannot be word for word.
I do not take personal responsibility for what I say now, because I am a beginner. But my wife is Vietnamese and a natural Vietnamese speaker. She says that có is not a pair with không, but only emphasizes the verb, muốn in this case. Compare with: you do want to return to Vietnam, right?
This isnt quite right... For an implicit or a "leading question" you shoild use a " có.... phải không? " structure (literally translated as " .. is correct, no?"). The correct question should be: "Bạn có muốn trở về Việt Nam phải không? "
Yes, you can. It's a "có... không? " binary interrogative. ..i.e a yes/no question form. So you can answer like this.
I'm a little unclear as to when I need to add không to the end of a question. Can anyone clear that up for me not?
Không at the end of a sentence changes a statement into a question. So in this case không equates to "Do you want to return to Vietnam? Without không it would be a statement, You want to return to Vietnam.
Try to think of không at the end of a sentence as being the English equivalent of adding don't you/isn't it etc... at the end of a sentence. Statement - You go to school. Question - You go to school, don't you? Statement - That's a nice car. Question - That's a nice car, isn't it? I hope that helps.