When you take the Study action, you make an Intelligence skill check (skill depends on creature type below) against another creature to uncover information about it.
Each creature or group of creatures has a total of 3 pieces that can be uncovered. Each piece of information has a different DC, and if you unlock one piece, you unlock all pieces of a DC lower than it. The DC of the first piece of lore is 10 + CR, which each subsequent piece adding an additional 2 to the DC. If the creature is studied indirectly via documents, reports, clues, or during downtime, its CR is not added to the DC.
You can take the Study action against a creature if you can see it, or if you have access to information about it, such as documents, experienced witnesses, or clues in the world.
Skill per Creature Type
Skill
Creatures
Arcana
History
Investigation
Nature
Religion
Study