A bad book club question sounds like it was written by somebody trying to prove they finished the novel.
A good one opens a door. It gets people talking about motive, sympathy, structure, or the one scene they cannot stop replaying. It gives the room somewhere to start without telling anybody where they have to end.
I still love that moment when one smart question changes the whole conversation. Suddenly the book gets larger, stranger, or more personal than it looked 5 minutes earlier.
That is part of the fun. Reading alone is one pleasure. Watching a room of readers build a better answer together is another.