Talk to Raminus Polus and he will tell you that you must have a mage’s staff before you can be promoted further. The wood for this staff must come from a grove near Wellspring Cave, northeast of the Imperial City, so he instructs you to go there and talk to Eletta or Zahrasha. Travel to Wellspring Cave and enter it to find the body of Zahrasha just inside. Take the Wellspring Cave Key off of her body and travel through the cave, killing the necromancer that you find there. Exit the cave to find yourself on an island in the middle of the lake.
There are a number of other necromancers on the island who you will have to kill. If you’re having trouble with them, you can duck back into the cave and only one will follow you, allowing you to pick them off individually. Once they’re all dead open the chest and retrieve the Unfinished Staff. Return to the Arcane Sanctuary and speak with Raminus Polus. He will direct you to Delmar in the Chironasium. He will ask you to pick out the type of enchantment that you want in your staff and then wait for twenty-four hours. Once you’ve picked up the staff from Delmar, talk to Raminus again and he will promote you to Journeyman.