-at-
to be at (someone) -
where it's at - the place where the most interesting or exciting things happen: "Emma says that Rome is definitely where it's at now."
-in-
used to indicate inclusion within space, a place, or limits (for example): "walking in the park"
"speak in English"
-on-
like preposition - "a painting on canvas"; "mounted on cardboard"; "legs on a chair".
"depends on my mood"