The statement "he can see nothing, can he?" sounds extremely unnatural (or like something someone would say when speaking extemporaneously), and it's a bit confusing even for me, but the most logical answer to an English native speaker would be:
B. No, he can't. He is blind.
A major clue is the tag question, "can he?" (not "can't he?"). The answer is "no, he can't."
A better test question would be "He can't see anything, can he?"