...You were a what? A supervisor?
...It was a what? A Toyota?
My contention is that these questions are just turned around from what they should be. Instead of "What were you?" and "What was it?" the order is reversed. It is just bad grammar (to which we apply good punctuation).
Whenever the question comes up, there is a tendency to want dashes. They are just not necessary Just put a question mark. The question is "What were you?" or "You were what?"
Happy punctuating!
Margie