outside at the Redeemed temple near Utopolis (Pos: 825 815) which is who you dealt with during the garden key quest. Use the chat option about his needing more help, show him your garden key when requested and continue through the chat sequence. He'll then give you a new mission which sends you around to kill the named Unredeemed mobs you tagged in the garden key quest. After you kill one the mission will be updated with your next target and each include a way point as well which makes things easier.
If you're doing this by yourself at around level 100 or lower while the mobs you're sent after may not be a problem the social aggro you bring down on yourself once you attack them may be. So be careful or bring help.
The local Unredeemed mobs are around level 85 while your three targets are all level 70.
They're conveniently located all in one spot, just be sure to kill them in the right order.
When you get back let him know you completed your task but you're worried after finding the Briefing which outlines an Unredeemed attack on the Redeemed in Elysium. After you hand the Briefing over you'll get your sanctuary key, some XP/SK, creds and two daily mission like XP/SK rewards (no tokens though). The XP/SK and cred rewards scale based on your level.