[skills]

Knowledge (Int; Trained Only)

Table: Knowledge Skill DCs
Task Knowledge
Skill
DC
Identify auras while using detect magic Arcana 15 + spell level
Identify a spell effect that is in place Arcana 20 + spell level
Identify materials manufactured by magic Arcana 20 + spell level
Identify a spell that just targeted you Arcana 25 + spell level
Identify the spells cast using a specific material component Arcana 20
Identify underground hazard Dungeoneering 15 + hazard's CR
Identify mineral, stone, or metal Dungeoneering 10
Determine slope Dungeoneering 15
Determine depth underground Dungeoneering 20
Identify dangerous construction Engineering 10
Determine a structure's style or age Engineering 15
Determine a structure's weakness Engineering 20
Identify a creature's ethnicity or accent Geography 10
Recognize regional terrain features Geography 15
Know location of nearest community or noteworthy site Geography 20
Know recent or historically significant event History 10
Determine approximate date of a specific event History 15
Know obscure or ancient historical event History 20
Know local laws, rulers, and popular locations Local 10
Know a common rumor or local tradition Local 15
Know hidden organizations, rulers, and locations Local 20
Identify natural hazard Nature 15 + hazard's CR
Identify a common plant or animal Nature 10
Identify unnatural weather phenomenon Nature 15
Determine artificial nature of feature Nature 20
Know current rulers and their symbols Nobility 10
Know proper etiquette Nobility 15
Know line of succession Nobility 20
Know the names of the planes Planes 10
Recognize current plane Planes 15
Identify a creature's planar origin Planes 20
Recognize a common deity's symbol or clergy Religion 10
Know common mythology and tenets Religion 15
Recognize an obscure deity's symbol or clergy Religion 20
Identify a monster's abilities and weaknesses Varies 10 + monster's CR

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. Below are listed typical fields of study.

Check

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. Many of the Knowledge skills have specific uses as noted on the side table.

Action

Usually none. In most cases, a Knowledge check doesn't take an action (but see "Untrained," below).

Try Again

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.

Untrained

You cannot make an untrained Knowledge check with a DC higher than 10. If you have access to an extensive library that covers a specific skill, this limit is removed. The time to make checks using a library, however, increases to 1d4 hours. Particularly complete libraries might even grant a bonus on Knowledge checks in the fields that they cover.

Knowledge Skill Unlocks

Pathfinder Unchained
With the Signature Skill feat and 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.

Phrenology (Occult Skill Unlock)

Occult Adventures
You examine the skulls of intelligent creatures to analyze the subjects' psychological attributes, since the shape of the brain influences the shape of the skull.

Requirement

Characters capable of casting psychic spells or who have the Psychic Sensitivity feat gain access to this skill unlock. A character must be trained in the appropriate skill to use that skill’s unlock, even if the skill can normally be used untrained. It’s impossible to take 10 for an occult skill unlock. Occult skill unlocks require intense concentration and strenuous effort, so the amount a character can use each skill unlock is limited to once per day or per week. This limit is for all uses of the skill unlock. 

Task DC
Determine race and age 10
Determine gender 15
Determine alignment 15 + creature's HD 
Determine class 20 + creature's HD
Determine level or HD 25 + creature's HD
Check

Once per day, you can use your fingertips to examine the shape of a creature's skull. Reading a creature's skull requires 1 minute of concentration and scrutiny while you physically manipulate the skull. This technique can be used on a willing, helpless, or paralyzed creature, or on decomposed remains (as long as the skull is intact or can be pieced together). This skill can't be used on creatures without discernible skulls, such as constructs, elementals, oozes, or plants. After the minute is up, the GM attempts a secret Knowledge (arcana) check. The DC is typically modified by the subject's Hit Dice. With a single check, you determine all the information whose DC you meet. For instance, if you had a result of 22 when examining a creature with 2 HD, you would learn that creature's race and age, gender, alignment, and class, but not its level or HD. A dead creature's skull uses the HD the creature had when alive.

Action

Reading a creature's cranium requires 1 minute of uninterrupted study.

Try Again

Yes. Reexamining a skull may provide new insights. You can attempt only one such check per day.

Recall Intrigues

Spymaster's Handbook

Task Knowledge
Skill
DC

Identify a class feature from a class that grants arcane or psychic spells

Arcana 10 + class level when feature is granted*

Identify a class feature from a class with access to the druid or ranger spell list

Nature 10 + class level when feature is granted*

Identify a class feature from another class that grants divine spells

Religion 10 + class level when feature is granted*

Identify a class feature from any other class

Local 10 + class level when feature is granted*

Identify a combat feat being used

Local 10 + character's level

Identify a metamagic feat being used

Arcana 10 + character's level

Identify a teamwork feat being used

Nobility 10 + character's level
Identify any other feat being used Local 15 + character's level

You can identify feats and the class features of various classes with successful Knowledge checks when you observe the feats or class features being used.

Check

You can attempt a skill check to identify a feat or class feature when you observe it in use, similar to how Spellcraft can be used to identify a spell. The feat or class feature must have some observable effect in order for you to attempt the Knowledge check. For example, you can't see the internal determination of Iron Will, so this ability can't identify that feat. In general, if a feat or class feature creates a noticeable effect (such as the extra attack from using Cleave) or has a variable modifier a character must choose to use (such as Arcane Strike, Combat Expertise, or Enlarge Spell), it can be identified. If it creates a static bonus (such as Dodge or Lightning Reflexes), there's no telltale sign to give it away.

The Knowledge skill required to identify a feat or class feature varies depending on the type of feat or class feature to be identified and is outlined in the Recall Intrigues (Knowledge) table above, along with the DCs of such skill checks.