The following page describes how to unlock new hero skills in Darkest Dungeon 2 , what hero's Shrines are, how many unlockable skills are available, and how many skills a hero can use.
In Darkest Dungeon 2, heroes can unlock up to 11 new skills. At the beginning, everyone has only 5. They can also only use 5 skills during the game. Outside of combat, however, you can turn the skills on and off freely in the character panel. Further skills are always unlocked in the same order. Skills unlocked in one game will be available in the next - only Mastery points don't transfer to further games.
Skills can be unlocked by visiting Hero's Shrines (marked with a bell on the map). In each such Shrine, you choose one hero to pass a test. Sometimes you'll simply hear the hero's story and move on. In other cases, some of the allies (with specific skills) will have to prove their worth in mini-games. The hero has to visit the Shrine 5 times to unlock all skills - on the last level, they will unlock two.
These skills have their own rules: sometimes you will see information about the task in the upper left corner of the screen, sometimes you have to guess yourself. More information about the mini-games can be found in the skill description in this guide.
Aside from the new skill, you will also receive a Mastery point. Of course, only if you manage to unlock the skill.