Arelion's Journal once belonged to Arelion, it details his escapades with a young female blood elf.
Arelion's Journal is looted from Arelion's Knapsack, found at the Pools of Aggonar in Hellfire Peninsula. The knapsack is hanging from the branch of a bramble in the center of the pools.
It can also be dropped by any of the ooze monsters about.
This item is a quest objective of  Arelion's Journal.