Using knowledge to learn about monsters

[Gunslinger]

You cannot take 20 on a knowledge skill. In both 3.0 and 3.5 it assumes that you try whatever you are attempting to do 19 times before you finally roll that 20. Therefore it cannot be used with a skill that does not allow retries. However, taking 10 does not seem to work the same way (i have no idea why), so that still might work.

 

[Li Shenron]

I am actually very generous when players use Knowledge to get hints about monsters, and give more than "a bit" of information per 5 points over the DC. After all, for published monsters it's likely that the players already know more than what their characters can with a skill check.

You can take 10 on any skill. It just represents the fact that you are not being threatened or distracted.

Although the rules do not specifically prevent to Take 10 with Knowledge skills, I always strongly encourage not to allow it - only in the very specific case of how Knowledge skills work and what they are supposed to mean.

If you allow taking 10 on a Knowledge check, you can have some illogical situations (the reason being that you cannot retry a Knowledge check, so being threatened or quiet changes what you know). If you rule that Knowledge checks represent what you remember instead of what you know, then you can allow taking 10 and taking 20, as well as retrying (although you may want to introduce some time delay between checks).

If you use Knowledge skills for research, then it otherwise makes very sense to allow all of the above as well.