In a debate, a speaker comments on the questioner's competence instead of answering the question. What improper strategy is this?

Correct answer: Personal attack

The governing concept is relevance and respectful argument. A debate should address the claim, evidence, or reasoning in the question. Attacking the questioner's competence shifts attention from the issue to the person and supplies no answer to the original point; this is a personal attack, often called an ad hominem tactic. A rebuttal, example, or clarification would engage with the subject instead.