Napisał SRD: Knowledge skill

In many cases, 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 HD. 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.

Action
Usually none. In most cases, making a Knowledge check doesn’t take an action—you simply know the answer or you don’t.