SOS Encounter: Route 12 (15%, Only in Sun & Moon), Blush Mountain (15%, Only in Sun & Moon), Mount Hokulani (15%, Only in Sun & Moon) + 2 more
Surf: Poni Plains (20%, Only in Ultra Sun & Ultra Moon)
Its base catch rate is 30 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 Love Ball or Heal Ball.
Evolution: Happiny → Chansey → Blissey.
Chansey in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)