When the witness repeats the question or part of the question and then answers it, use a question mark after the question and let the rest of the answer stand on its own.
…Q Was it after 10:00 that he called that night?
…A Was it after 10:00? Yes.
…Q What was the attire for the meeting?
…A What was the attire? It was business attire.
…Q Were you there alone?
…A Was I alone? No.
…Q Do you own a personal computer?
…A Do I have a computer? Of course.
If what he repeats is not in the form of a question, then it can take a comma or a question mark, depending on the intonation.
…Q Did you join him for dinner after that meeting?
…A For dinner, yes.
…A For dinner? Yes.
…Q Did you buy a new car during that time period?
…A A new car, yes.
…A A new car? Yes.