A new feature of Pokémon Sun & Moon is what is called Evolution Moves. These moves are moves that a Pokémon is completely guaranteed to learn upon the evolution. This means that if you miss the standard level to evolve a Pokémon, you won't necessarily miss a signature move or a move that fits it well. These moves are commonly at the top of a Pokémon's learnset, designated as a Level 0 move.
There is, however, an issue with Evolution Moves at time of writing. If you evolve a Pokémon at a level when the evolution would learn the move which is also a Level 1 Move, and it has an Evolution Move, then the Pokémon won't learn the standard move. For example, Abra evolves at Level 16 and Kadabra is meant to learn Confusion at Level 16, but it also has the Evolution Move Kinesis. Due to this, the Kadabra won't try to learn Confusion. It is unclear if this is a glitch or an intended consequence.
What happens is that Kadabra will always try to learn Kenesis when it evolves from Abra. However, at level 16, it also tries to learn Confusion. What appears to be happening is that an evolution move overrides a level-up move, so Kadabra learns Kenesis instead of Confusion. If you want a list of evolution moves, look here.
I hope this answers your question :D