Silcoon's best moveset in Pokémon GO is Poison Sting and Struggle, with 3.45 damage per second, and it can deal 33.4 damage before Silcoon faints. This is true when battling in neutral weather.
All Silcoon movesets ranked
Here is a complete list of Silcoon movesets in Pokémon GO, ranked by their DPS and TDO. You can change the weather and the opposing Pokémon.