The Witcher 3: Wild Hunt Edit
Aldert may be met during the Prologue at the tavern in White Orchard. Unlike the rest of the populace, he seems eager to reach the front lines of the war between the Northern Kingdoms and Nilfgaard, in order to describe and catalogue it in what he hopes will be his magnum opus.
After the Prologue, Aldert can be found hanged at the Hanged Man's Tree in Velen. Beneath his body, you can pick up and read the book he was writing, and the gwent card he had if you didn't beat him in White Orchard.