If you don't know how to do quest some information here
Dark Elven Tetrarch Vellior has insomnia due to continuous nightmares. A creature called a succubus is the source of the nightmares, and you will be asked to defeat the dream catching succubus 'Merkenis' at the School of Dark Arts.
Level 21
Start Location Dark Elven Village
Start Npc Tetrarch Vellior
Races Dark Elf
Classes All
Repeatable No (Solo)
Speak to Tetrarch Vellior to begin the quest.
Travel to the School of Dark Arts (which is southeast of the Dark Elf village). In the center of the dungeon, a succubus spawns called Merkenis. Kill her to receive the quest item (you MUST get the last hit).
Return to Tetrarch Vellior to receive your reward.