Hello,
The comments section in here should provide you with a list of the reputations that count towards the achievement! I hope it is useful for you.
Finding specifically which characters did the grind to Exalted might be a bit trickier. Generally when your character is rewarded with an Exalted reputation, if you go to the achievement panel and hover the mouse pointer over the icon/shield it will show you a pop-up saying “Earned by CharacterName”. If your character has not earned this achievement, but it is still earned, the pop-up will say “Not Completed by CharacterName”. That may help you determine which character did the achievement!