This quest is given by Eben Stonearm at Timber Falls in Nektulos (+497.70, -1456.22).
He asks you to kill 10 Mist Grinnin in the Nektulos Forest. Elder Mist Grinnin also work. After killing them all return to Eben Stonearm.
The reward is your choice of 5 salves or 5 potions of marr (power restoring potions). Completing this quest also opens up the "Lending a Hand" quest.