You are educated in a field of study and can answer both simple and complex questions. Like the Craft, Perform, and Profession skills, Knowledge actually encompasses a number of different specialties.
Many of the Knowledge skills have specific uses as noted on Table: Knowledge Skill DC's.
Below are listed typical fields of study.
Answering a question within your field of study has a DC of 10 (for really easy questions), 15 (for basic questions), or 20 to 30 (for really tough questions).
You can use this skill to identify monsters and their special powers or vulnerabilities. In general, the DC of such a check equals 10 + the monster’s CR. For common monsters, such as goblins, the DC of this check equals 5 + the monster’s CR. For particularly rare monsters, such as the tarrasque, the DC of this check equals 15 + the monster’s CR or more. A successful check allows you to remember a bit of useful information about that monster. For every 5 points by which your check result exceeds the DC, you recall another piece of useful information.
Usually none. In most cases, a Knowledge check doesn't take an action (but see “Untrained,” below).
Retry? No. The check represents what you know, and thinking about a topic a second time doesn’t let you know something that you never learned in the first place.
About This Section Optionally, a character who reaches 5, 10, 15, or 20 ranks in a skill unlocks various bonuses and abilities unique to that skill. The unchained rogue uses these rules extensively, but others can gain access to them with a new feat.
In this system, characters unlock additional abilities when they attain 5, 10, 15, and 20 ranks in a skill. The skill unlocks system interfaces with the unchained rogue to make the rogue the true master of skills.
Skill unlocks give characters new abilities and ways to use their skills upon reaching 5, 10, 15, and 20 ranks in a skill. Any character with the Signature Skill feat can earn skill unlocks for a single skill, and they are a prime feature of the revised version of the rogue who uses her rogue's edge ability to gain skill unlocks for several of her most iconic skills. Alternatively, you might make skill unlocks a universal part of the game, but you should be aware they add significant power and flexibility to skills, so giving them for free to all classes would grant power boosts to other highly skilled classes such as the investigator and bard, particularly in comparison to the rogue. Another alternative is to eliminate access to the Signature Skill feat, limiting skill unlocks to rogues and rogues alone.
With sufficient ranks in Knowledge, you earn the following.
5 Ranks: When you successfully identify a creature, you gain one additional piece of information for every 5 ranks you possess in that Knowledge skill.
10 Ranks: When you successfully identify a creature, you gain a +1 competence bonus on attack rolls, opposed ability checks, skill checks, and caster level checks against creatures of that kind (e.g., glabrezu demons, but not other demons or evil outsiders) for 1 minute. This bonus increases by 1 for every 5 ranks beyond 10 you possess in that Knowledge skill.
15 Ranks: When you fail a Knowledge check, you can reroll the check at a –10 penalty. The competence bonus above also applies to saving throws against exceptional, spell-like, or supernatural abilities used by creatures you identify.
20 Ranks: Whenever you attempt a Knowledge check, you can roll twice and take the better result.