J’Zhirr enters one of the black buildings that littered the Soul Cairn. It has a glowing tower and at the bottom of it are some motionless people. A beam of light exits from them and enter the tower. J’Zhirr tries talking to them but they ignore him.
As this one puzzles about what to do next, he hears Serana cries out. J’Zhirr immediately runs to help and sees that she is fighting a headless warrior. He must be the one guarding this tower. After we defeated him, the tower turns dark and the people disappear.
There seems nothing else that we can do here.