Chapter 11.
Maw of the Abyss.
After the first really annoying Boxed Phalanx battle, follow the trail until you get to the pocket that's got four Hoplites in it. Fight them, and keep looking for the left turn that's just beyond that point.
Take the left, and fight all the battles until you get to where the Juggernaut hides. Don't fight the juggernaut.
Don't even get close to the damn door. If you do you will trigger the cut scene that initiates the juggernaut battle.
And you will die instantly.
Instead, turn around and run back down the path.
The last two battles you fought before the juggernaut, the five hoplites and the trio of Cryohedrons, will NOT come back.
However, the combined groups of two hoplites and three Cryohedrons will have respawned.
Fight them, defeat them, and pocket 5500 CP.
Turn around and run back to the area in front of the Juggernaut door.
Now run back.
The combined groups of two hoplites and three Cryohedrons will have respawned.
Fight them, defeat them, and pocket 5500 CP.
Turn around and run back to the area in front of the Juggernaut door.
Now run back.
Repeat.
For as long as you like.
You can literally grind enough points here in roughly two hours to fill out all the available gems in the Crystarium for a character.