Find Lantalir in the Druids of Arakas and talk to him. Following the usual keywords name, job, function, you will learn that he is looking for Feylor's Book.
To find the book, go to the ancient Dwarven City. To access it, you must go through the Arakas Maze.
This maze is located in the cave whose entrance is southwest of the RST, near the kraanians.
Go through the maze, and once on the other side, look for a regular-looking chest.
You will need an iron key to open it (the key will not disappear).
The chest will drop the famous Feylor's Book on the ground, which you then need to return to Lantalir.
Note that you can also find the book first and bring it directly to Lantalir without starting the quest beforehand.
Reward: