It comes from the fourth task in Arthicrex called "To Serve Sporali." This is a group task and follows three solo progression line tasks in Arthicrex. The npc for this task is Grgald Elderhammer. Not confirmed whether or not you have to do the entire line to get spell, though I imagine you will have to like I did. Good luck and have fun! It's actually one of the easier lines in Underfoot.
Edited, Dec 12th 2009 3:20pm by neraforesta