Yamper's best moveset in Pokémon GO is Bite and Thunder, with 6.02 damage per second, and it can deal 73.7 damage before Yamper faints. This is true when battling in neutral weather.
All Yamper movesets ranked
Here is a complete list of Yamper movesets in Pokémon GO, ranked by their DPS and TDO. You can change the weather and the opposing Pokémon.