weapon name is "Black Abyssal Amulet", you can obtain this weapon through a lvl 55 quest in Altinova from the NPC named Konah at the arena.

here is the image for the location of the NPC:
https://cdn.discordapp.com/attachments/386137745313103872/389990092665520138/unknown.png

Do note that there is a limit of 1 per account so choose wisely which character you want this weapon for.