
One effect from any other piece of armor ( boots, pants, helms / spirit stones / voodoo masks / wizard hats, pauldrons, bracers, chest armor / cloaks, gloves, or belts / mighty belts). One effect from either a weapon ( one-handed or two-handed) or an off-hand item ( quivers, mojos, sources, phylacteries or shields / crusader shields). While characters may only have up to 3 of them active, they can store all acquired essences within the cube, swapping them at any time when in town without losing essences they override. The extracted abilities are stored within the Kanai's Cube, and are not lost if replaced.
They are extracted via a recipe known as Archive of Tal Rasha.
Kanai's Cube powers are passive abilities extracted from various legendary and set items in Diablo III: Reaper of Souls.