On this page of the Elex 2 guide, you will find a walkthrough of the Broken Trap quest. You receive this quest from Ahran (his exact location is listed below), while the mission itself requires you to kill 5 Nervous Biters.
Starting the quest
You'll find the quest giver, Ahran, to the west of the Fort. We've marked his location with a red circle on the picture above. You can also activate a fast travel point in the area.
Killing the Nervous Biters
After you talk to Ahran, the game will mark the area where the Biters are on your map - go there.
Once you arrive you must fight the monsters. They're very weak and your basic gear should be enough to dispatch them. Killing all the enemies completes the mission, but you should return to Ahran anyway - he'll reward you with 200 Elexit crystals.