Must one repeat the prayer upon feeling flatulence and suppressing it, then smelling an odor without being certain of its emission? And what is the ruling on emitting flatulence in the mosque?

If you smell an odor and are certain that it emanated from you, then your prayer has become invalid and must be repeated, because the ruling hinges on certainty of the impurity (hadath). However, if it is merely a matter of waswasah (whispers/C.D.O.), do not pay attention to it, and your prayer is valid. Passing wind in the mosque is permissible, but it is better to avoid it.