Don’t ask, TAKE sufficient close up pictures FIRST at the debate so they can’t be denied. Then make some interesting comments about his and Ann’s rings. Get someone else later to ask about the Obamas’ rings to balance a nice, bipartisan human interest story.
Asking during the debate puts it on MSM where it can't be ignored. But it also puts Obama in the position where he's unlikely to lie about it since he's wearing it on national TV, and he doesn't know what pictures people have already.