This becomes available available completing “Revenge of the Nora”. Talk to Sona in Mother’s Crown. She’ll ask you to deliver the signal arrows to Orn in the unmarked watch tower south of the encampment.
Follow the mission marker and climb the rocky slope using the climbing holds until you reach the tower. Talk to the young man named Orn to deliver the signal arrows. Loot the supply cache then fast-travel back to Mother’s Crown to report back to Sona.
You need to reach her at the watchtower on the rocky cliff beside the northern gate. Use the climbing holds and ledges to climb up. Talk to her to complete the quest.