Before you can unlock this, you'll need the following skills in the Magic tree:
Mage Sight -> Enchanter -> Dread Warlock -> Able Sorcerer + Runic Mastery
Then, create the following spell using runes: ᛒᛉᚢᛏ
There are likely other combinations available, but I haven't found any that work. By the time you have enough skill points and enough days have passed to unlock the skills, you'll likely have all the runes required. If you can't unlock the skills, keep playing and doing main missions/faction quests - eventually they will become available.