Gift: Lake of the Moone (Only in Moon & Ultra Moon), Lake of the Sunne (Only in Sun & Ultra Sun)
You won't find Cosmog in the wild in this game — you get it as a gift.
Looking for Cosmoem? It isn't found in the wild in this game — evolve Cosmog (Level 43).
For the look, the best colour match is Poké Ball.
Evolution: Cosmog → Cosmoem (Level 43) → Solgaleo (Level 53) · Lunala (Level 53).
Cosmog in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)