Reaper of Souls - Achievement Guide - Field Research

0:00 - The Souls of Westmarch - dropped by Kasadya in the Zakarum Cathedral.

0:16 - Malthael's Plan - after you've obtained the three Siege Runes in the Battlefields of Eternity, and turn in the quest to Ttyrael at The Siege Outpost, he'll drop the book (no, you don't kill him!).

0:52 - Adria's Note - dropped by Adria.

All parts of The Path of Wisdom can be found in The Pandemonium Fortress, Level 2.
1:08 - The Path of Wisdom, Part 1
1:32 - The Path of Wisdom, Part 2
2:04 - The Path of Wisdom, Part 3
2:28 - The Path of Wisdom, Part 4
3:01 - The Path of Wisdom, Part 5
3:30 - The Path of Wisdom, Part 6

4:06 - Uzarel's Trap - look in the Westmarch Commons for a Resplendant Chest in a small, gated area. Try to loot the chest to start the event "Walk in the Park." Kill the enemies, and the book will drop (note the book is called "It's a Trap").

4:21 - Miser's Will - found in Miser's Satchel, within Miser's Hovel (Westmarch Commons).

4:44 - The Great Weapon - complete the "The Great Weapon" event (Battlefields of Eternity).

5:20 - Grand Maester's Journal - found in the Maester's Satchel, within the Secret Templar Stronghold, a location you visit during Kormac's side-quest. Look to the Kormac N' Cheese achievement guide on how to begin Kormac's side-quest:

5:47 - The Last of the Ancients - in Act 5.4 (The Witch), enter the Blood Marsh and the Paths of the Drowned, activate three markers to discover the "correct" Passage to Corvus. Now, ignore it - search the other, "wrong" passages, and hope to get an event called "The Last Ancient." Kill Kalmor, and search the Ancient Satchel for the lore book.