You can see what chapter you're on in the game. I think it summarizes each chapter in the Datalog. You can also see what chapter you're on when you load or save the game.

Anyway the grind spot i'm talking about is after your last party member gets his/her eidolon. Read on for an exact location...

[SPOILER="very minor spoilers"]There are 5 "Pulsework Gladiators" (gold colored walking machines) in Taejin's Tower at the bottom of the Fifth Tier stairway. Lead them to the stairs, wait for them to turn around and charge from behind for a Preemptive Strike followed up by a Quake for everyone to get staggered (these also don't attack while staggered). Ravager AOEs kill them off quickly. I think I've been able to kill all five in less then 30 seconds.

To force them to respawn, head up the staircase, run through room to the outer walkway (easily avoid the mob) then come back down. I noticed that sometimes I had to go up and down the stairs once or twice for them to show back up. Still, the whole process takes like 90 seconds.

If you have trouble with the boss in this area, you can easily come back to this spot.
[/SPOILER]