A Period or a Question Mark?

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.

Happy punctuating!