After talking with the Necromancher i received the related quest.
Underground Prisoner
A black sorcerer, imprisoned in a crypt centuries ago by war mages, has accumulated strength and is ready to perform a destructive ritual. It is necessary to stop the evildoer, who was become a Resurrected Ghoul.
Current goal: Having killed the Fazgrod Resurrected Ghoul [12] in the Clan Burial Grounds, obtain the Deathly Amulet and bring it to Koeshu in the Clan Burial Grounds.
The Ghoul was nowhere to be found yet.
So, i went to Forgotten Library and bought:
Deathly Heart Guidebook hoping that it might shine some light.
Yet the wiseman does not accept it in order for me to be able to learn the book.
I guess more people will have the same problem.
Thank you in advance,
wanderer