Knowledge skills for monster threat assessment.

I'm going to allow checks on Nature/Religion/Arcana/History/Streetwise etc to assess monster threat level within the following bands. Threat level will be for typical representatives, it's possible that a particular unusual creature could fall outside the band on either the high or low end.

Low Heroic: 1-3 - eg goblin
Heroic: 4-7 - eg orc
High Heroic 8-10 - eg ogre
Low Paragon 11-13
Paragon 14-17
High Paragon 18-20
Low Epic 21-23
Epic 24-27
High Epic 28-30+

Whether the check DC is easy, medium or hard will normally depend on how famous or obscure the monster is; assessing dragons is easy, while assessing some obscure creature from MM3 might be hard, or even impossible if no one has ever reported meeting such a thing before.
A failed check close to the DC may get vague information, within a 2-3 band spread, while a badly failed check means you have no idea.