Is there a word for the act of answering a question in painstaking detail in order to mock the fact that the person asking cannot possibly usefully employ the information you are giving him or her?

Yes, the term "pedantry" often describes the act of providing excessive detail or focusing on trivial points, which can be used to mock or belittle someone's understanding. Another related term is "sarcasm," especially when the detailed response is intended to highlight the futility of the question. Additionally, "over-explanation" can refer to the act of elaborating unnecessarily, particularly when the audience may not find the information useful.