1. In the basement's metal chest right after the skeleton(s) in Majula's Mansion, key acquired from Cale the Cartographer, in the mine right after the Cardinal Tower (Forest of Fallen Giants), watch out for the rolling boulder!
2. Obtained from dialogue with Crestfallen Saulden. (After you bring 4 people to Majula, when he will thank you for the company).
3. In Drangleic Castle near the Central Castle Drangleic bonfire - must activate the elevator - middle chest where you get the King's key.
4. In Lost Bastille inside a wooden chest behind a Pharros' Door. From the Heide Knight, go down the ladder, break the wooden planks on your right, defeat the 4 dogs, then the 3 hollows. Use a pharos lockstone. (Can respawn the soul vessel by using a bonfire ascetic, although using an ascetic here requires that you have defeated the Lost Sinner). Note that even if the chest itself is destroyed, you will still get a Soul Vessel instead of Rubbish.
5. Inside the Memory of Orro area after the Pursuer. Go right to the first hallway, go outside and immediately turn right, you should see a lootable body, it contains a Soul of a Great Hero and a Soul Vessel
6. Inside the Undead Crypt, fall to a platform in the room with the lowerable bridge (opposite the one leading to the Crushed Eye Orb).
This video shows you how to get all the Soul Vessels. Soul Vessels allow you to redistribute your soul points in the Things Betwixt from the old firekeepers. If you found this helpful, be sure to Subscribe and like for more!