Duskull's best moveset in Pokémon GO is Hex and Ominous Wind, with 4.43 damage per second, and it can deal 54.5 damage before Duskull faints. This is true when battling in neutral weather.
All Duskull movesets ranked
Here is a complete list of Duskull movesets in Pokémon GO, ranked by their DPS and TDO. You can change the weather and the opposing Pokémon.