Speak to Hashu Whelegrind at -150, 14, 189 at the entrance camp in The Eidolon Jungle to begin this quest.
Use the attuner on soullights in the Eidolon Undergrowth.
They are wisps that fly up near the leaves of trees.
These mobs cast a spell called "Spirit Barrier" on themselves when aggroed which can be interupted. While this buff is active, the mob has a 95% damage reduction. The buff only lasts 6 seconds, but 25% of the time the mob is hit, Spirit Barrier will refresh on the mob for another 6 seconds. If the buff is on the mob, stop attacking it until it expires after 6 seconds, and then the mob will die very fast.