SOS Encounter: Brooklet Hill (30%), Malie Garden (30%)
Its base catch rate is 60 out of 255 (higher is easier); the catch rate calculator works out your odds with each ball. For the look, the best colour match is Timer Ball.
Evolution: Goldeen → Seaking (Level 33).
Seaking in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)