Similar to the RAW pathfinder, though this clarifies some things.
Knowledge Checks vs Monsters in Pathfinder:
Knowledge Skills are one of the most useful skills a Pathfinder can have. They allow you to identify the qualities and powers of enemy creatures (or supposed friendly ones) as a free action, on sight.
This is a small explanation for both GMs and for players when attempting to use a Knowledge Check.
-The DC for a Knowledge Check versus a monster is the creature's CR (often somewhere around its HD) plus 10.
-For a common monster (such as Goblins), decrease the DC of the Knowledge Check by 5.
-For especially rare monsters (such as the Tarrasque), increase the DC of the Knowledge Check by 5.
-The type of Knowledge Check depends on the monster.
---Arcana = Constructs, Dragons, and Magical Beasts
---Dungeoneering = Aberrations and Oozes
---Local = Humanoids
---Nature = Animals, Fey, Giants, Monstrous Humanoids, Plants, and Vermin
---Planes = Outsiders
---Religion = Undead
-A successful Knowledge Check yields the following information: the creature's Challenge Rating, Type, and Class ("This is a CR 2 Goblin Fighter")
-Additionally, success automatically grants you one of three categories of knowledge: Defense, Offense, and Special Abilities.
---Defense includes: Hit Dice Breakdown ("1 Hit Dice of Zombie, 2 Hit Dice of Cleric"), AC (Including Touch and Flat-Footed), Immunities, Weaknesses, Damage Reduction, Saves, and Defensive Abilities.
---Offense includes: Speed, Attacks (natural and constructed, but does not include weapons you cannot see on the enemy if they're not visible), Special Attacks, Spell-Like Abilities, Domains, Schools (Specialty and Opposition), and Bloodlines.
---Special Abilities includes: Defensive Abilities, Special Attacks, Spell-Like Abilities, Extraordinary Abilities, Supernatural Abilities, and Senses.
-For every 5 you exceed the DC of the check by, you may ask for another category of knowledge about the creature.
-You may not re-try a Knowledge Check against a creature or a creature of the exact same type and class.