Jack is dead.
The slave contract transmitted the last scene Jack saw before his death to Gong Qiying.
The murderers were two aggressively expressive young humans; it seemed a premeditated action. One stabbed Jack's heart with a knife, while the other cast some sort of spell that affected the soul, preventing resurrection.
These two were overwhelmed by passionate onlookers and then seized by the guards. The final image was of Jack falling face up, surrounded by a crowd of spectators.
Gong Qiying wasn't sure if it was an illusion, but behind the killers, two transparent threads flashed past; they appeared so briefly that he doubted his own eyes.
"..."
Nevertheless, he was somewhat angry.
Whether those two had a grudge against Jack or there was some other cause for their actions, he had no idea. All he knew was that his recently cultivated subordinate had been killed, which was akin to a slap in his face.
He must find these two after going out and give them a thorough scolding.