Next to the Dragon-Kin Mausoleum bonfire in Archdragon Peak, there is an infinitely respawning enemy that gives 5280 souls for every kill when using the Covetous Silver Serpent Ring and the Shield of Want!
►918,000+ souls per hour!
►153,000+ souls per TEN MINUTES!
If you do not have the Archdragon Peak unlocked, and its tricky to find, first you need to warp to the Irithyll Dungeon. Make your way to the bottom of the dungeon to this area with all the mages with iron brands. Walk outside, and use the path of the dragon gesture on the prayer rug next to the other dragon statues, and after a few seconds you will get warped to a new area. The soul farming area is immediately after the first boss fight of the new area.