Since you are making the enamine from the iminium ion, I think enolization of the aldehyde is possible. I'd have it add to the carbonyl group. Since the groups attached to it are different, I'm expecting a selective addition. Also, since it is heated, elimination of water. Now that I am thinking about it, I would tell students that "heat" was a key to expect elimination. Also, could the problem have an error, such as a missing reagent?