I am making the Braised Cabbage. What does it mean to render the fat and do I leave the Pancetta in - or am just keeping the "renderings?"

To render fat means to chop up your bacon, pancetta, etc., and fry it to make the fat melt and become liquid. I don't know what your recipe says, but I would toss the crisp pancetta on top of the cabbage when you serve it.