CFI-I practical
You will cover the same stuff you covered for your instrument rating, so if you're relatively fresh off of that you should have the basics. You will go into more depth. I remember that my examiner emphasized systems.
Also, beware of FOI questions. Theoretically, for an add-on, examiners should not be asking FOI questions. You've already demonstrated your knowlege of the fundamentals of instructing for your initial CFI. Some examiners do it anyway. So much for "theoretically."
Flight will be something like an instrument ride out of the right seat. Never stop teaching. Some examiners like to do some flying, maybe to see if you can pick up their errors, but probably because they want some free hood practice.
Hope that helps. Good luck with your practical.