Celeb'hel the Elder - Act 2 Broken World Side Quest
Location: Calennor Wood (Start)
Closest Portal: N/A
Objective: Obtain both of Celeb'hel's Simulacra and return them to him
Reward: Celeb'hel's Ceremonial Garb or Celeb'hel joins your party
Celeb'hel the Elder is the first Side Quest you'll receive for Part 2 in the Broken World Expansion Pack. This quest will automatically begin after defeating Celeb'hel the Elder as a boss at the end of the In Search of Celia Story Quest in Part 1. You will not be able to do anything about this Side Quest until you meet Celeb'hel the Elder in the Calennor Wood very late during Part 2.
Upon meeting Celeb'hel the Elder in Calennor Wood you'll have to interrogate him about where he sent the remaining two simulacra. If you patronize him then you will not get the information you want out of him and you'll have to talk to him again.
The two simulacra that you need to find are in the Western Vai'kesh Forest as well as Calennor Stronghold. In order to reach the one in the Western Vai'kesh Forest you'll need to complete The Vai'kesh Side Quest and start The Vai'kesh (Part 2). Check out my sections below if you need additional information on where to find each one.
Simulacra #1: Western Vai'kesh Forest in the Small Vai'kesh Sanctuary where Rinerel is (Need The Vai'kesh (Part 2))
Simulacra #2: Calennor Stronghold - you'll pass through this area while doing The Second Familiar Surgeon Story Quest
Western Vai'kesh Forest - Simulacra #1 Location
Closest Teleporter: Western Vai'lutra Forest (South)
On my map above the location you'll want to visit is the red circle at the bottom marked Small Vai'kesh Camp. Celeb'hel's Simulacra can be found in a back room which will be locked to you until you are on The Vai'kesh (Part 2) Side Quest. During The Vai'kesh (Part 2) this camp will become hostile to you and you'll gain access to the rooms in the back.
You'll find Celeb'hel's corpse on the ground in a jail cell just before the large room at the southern end with Argir the Vai'kesh Prophet inside (pictured below).
Calennor Stronghold - Simulacra #2 Location
Closest Teleporter: Calennor Wood (North)
As aforementioned you'll pass through this area while doing The Second Familiar Surgeon Story Quest. To get to this dungeon you'll want to take the Teleporter to Calennor Wood (North) and then travel a tad bit north into the dungeon. The Vai'kesh (Part 2) begins by finding a corpse in this dungeon too, I recommend you grab that quest while you're here if you haven't already; you'll need it to find Celeb'hel's other Simulacra.
You'll find Celeb'hel's Simulacra in the central portion of Calennor Stronghold, use my map screenshot below if you need additional guidance.
After finding both Simulacra it'll be time to return to Celeb'hel who is found far to the east in Calennor Woods, the same location he was at the first time you found him. This time he will be joined by an Ancestor of the Azunites who will warn both you and Celeb'hel about using this spell.
You'll be given the choice to give Celeb'hel the soulstones or not. If you give him the soulstones and he performs the spell then he'll blow himself up and the quest will end. If you do not give him the soulstones he'll come to understand the mistake that he has made in his quest to save the elves and will offer to join your party as a companion.
Regardless of the choice you make you'll receive Celeb'hel's Ceremonial Garb as a reward for completing the quest.