Observational learning refers to learning from watching a demonstrator or how others do actions. So, the answer would be Sylvia's example because she watched her mom put a napkin on her lap, and then Sylvia copied her.
Observational learning requires observe an action and then learn to repeat the action.
The following answer choices do not involve observing:
Tristan is sure...
Kanu hears a song...
Trey plays with...
So the answer is Sylvia watches her mom put a napkin on her lap during restaurant dining, so she does the same.