Like all previous Pokemon Games from earlier Generations, The Alola Region has plenty of Move Tutors scattered throughout, willing to teach your Pokemon certain Moves. Each Move Tutor have something different they are willing to teach your Pokemon.
Move Tutors
Move Reminder: The Move Reminder, one of the most important characters in all of The Alola Region, can be found in the Pokemon Center at the top of Mount Lanakila. This character will reteach one of your Pokemon a move they have forgotten or you accidentally removed at some point, including Egg Moves they once kNew. A new ability for the Move Reminder is to teach your Pokemon a move they can level further along in their learnset.
Move Deleter: The Move Deleter can be found in the Hau'oli City Pokemon Center. But since HMs no longer exist, this character is only useful for certain Last Resort Movesets.
Pledge Moves Tutor: The Move Tutor that will teach any Starter Pokemon from any Region the special Pledge Moves (Fire Pledge, Grass Pledge, Water Pledge) is located in the Hau'oli Mall by Mr. Hype.
Ultimate Moves Tutor: The Move Tutor that will teach any Fully Evolve Starter Pokemon there Ultimate Move (Blast burn, Frenzy Plant, Hydro Cannon) can be found in the Hau'oli Mall by Mr. Hype.
Volt Tackle Tutor: The Volt Tackle Move Tutor is same person who will give you Pikachu's given Z-Crystal in Konikoni City. Volt Tackle can only be taught to Pikachu.
Secret Sword & Relic Song Tutor: The character that will teach your Keldeo Secret Sword and your Meloetta Relic Song can be found in the Hano Grand Resort. These Moves are necessary to change those given Pokemon's Forms.
Draco Meteor Tutor: The Draco Meteor Tutor can be found in the Seafolk Village Pokemon Center. She will teach this move to certain Dragon Types, as well as Arceus and Silvally when holding the given Plate or Memory that sees them also having the Dragon Typing.
Dragon Ascent Tutor: Also in the Seafolk Village Pokemon Center is the Dragon Ascent Tutor. He will teach your Rayquaza Dragon Ascent, which will in turn allow it to Mega Evolve.