Does anyone know when?
Kanai's Cube is obtained in adventure mode by talking to the ghost of Kulle who sends you to "Sescheron Ruins" -> "Elder Sanctum". It performs various tasks, among them extracting powers from legendaries. You can then use those powers without wearing the item.
The jewelcrafter combines jewels, same as the Horadric Cube in D2, but none of the other stuff. You'll probably have found him by now if you just played the story line as he is already located in Act II. He is named "Covetous Shen".