How to win the reward

The main requirement is to ask a meaningful question that require 2.5 minutes or more to explain the answer.

Strategy: listen intently to the presentation.  Look for a soft spot in the presentation, that is, an area that appears to have been abridged (not fully developed) during the delivery.  Politely ask the speaker to explain xxx in another way or in greater depth.  [Replace xxx with the topic of your question.]

In summary, your goal is to ask a question that will require 2 and a half minutes or more to fully answer.

Your professor makes the final determination regarding your win.  There is no appeal to the CS Department Chair or other administrative person.  If your question is answered in say 2 min 15 seconds, then you don't win.  It is as simple as that.