NOTE TO Franz: All of this information here in the 'Main Quest' lore pages is not known by the NPCs unless they are specifically mentioned to know about a piece of information.
The best place to start to find any book is the local library. By visiting the @Tarant University Library you can find out information by:
Becoming a member for 1500 gold (depending on your skills you can negotiate this down to 500 gold) and enquiring about the book. the librarian @Evelyn Thorne will give you a related book “@The Curse of T'sen-Ang”
Pickpocketing the book “@The Curse of T'sen-Ang” from the librarian @Evelyn Thorne
Killing the librarian @Evelyn Thorne and taking the book.
You may have already come across @Kendrick Wales in @Ashbury. If you can pass a difficuly pursuasion check and didnt anger him previously, he will give you the book “@The Curse of T'sen-Ang” as he wrote it.
Reading the book “@The Curse of T'sen-Ang”,you find out that there is one remaining copy of the rare book that inspired it, "@T'sen-Ang: Horror Among the Dark Elves". It resides in @Caladon in the @The Kingdom of Arland with Victor Misk.