What if you're an exempt employee that went 3 days over your paid leave time and was told you'd be docked for them (3 separate occasions - 1 day each) but then wasn't docked for them until the end of the year when all three days were docked from one payched, is that legal in NJ

If you missed FULL days that you were scheduled for, you can be docked for them. And it is not unusual for such docking to be done at the end of the year.