It's actually best done in the Test Servers if all you want is to get Class Points since there's no cap over there.
The higher level the monster the more points you get.

In the normal servers the points get scaled down to your level so if you are fighting a lvl99 monster in the normal servers you get points equal to a monster with the same level as yourself instead of 99.

This is actually why Yasaris used to be THE best place to farm CP before the nerf.
The snakes level was 200 instead of 20.