Grungol's PHs are the three "a penumbral coldain" mobs in the bridge area north of the throne room (one under the bridge and two above the bridge). You can do a "Find" (CTRL+F) for the quest NPC Kjelnor to get to this area.
Grungol has ~1.8 million hitpoints. Every 45 seconds, he casts "Desire of Hatred" (pull spell) on random target and focuses his attention on that target while ignoring aggro/hate effects from anyone else.
Location for your "kaelshard.txt" map file (note for all known Kael named spawn locations, see this quest entry):