In this quest he asks you to kill a monster called the "Ultimate Creature Boss" and collect one its limbs. The creature is in a cave called the Bone Burrow in the Orobas Fjords. Its location is shown on the wiki map (labelled as New Miners' Dig) below.
Upon entering the cave, descend the incline (south) to a T-shaped intersection. To the right (west) you will find a locked chest and several droxlerite ore veins if you are interested in looting them. To the left (east) and down another incline is the target of the quest, along with five venom stone ore veins. Upon killing the creature, you are prompted to choose one of four creature parts:
|Well-Preserved Remains of Arms
||Well-Preserved Remains of a Torso
|Well-Preserved Remains of a Head
||Well-Preserved Remains of Legs
Return to the tower and speak to Jonelath to complete the quest.