I’m not sure which one you mean. Is it this one? This? Or maybe this? Either way, the process is kind of the same. I just throw a pretty basic cylinder, a little thicker than normal. Then I slow down the wheel down and start working to make lopsided rings in it. I move up and down the side of the pot. At the end I use a rib (or other straight edge) to define the lines. Sometimes I leave them softer.
Hope this helps? If it was a different piece just let me know!