CFI materials
One of the first things you must learn as a flight instructor is how to use the PTS. Look at your CFI PTS. It will have a section of reference material upon which the practical is based. You will be responsible for knowing that material.
Having said that, no matter how well you might like Kershner, John and Martha, or any of the other commercial publications, the FAA pubs are always the final word on what to know, where to find it, how to do it, and how to teach it. For your CFI practical, you'll need such FAA materials as the Flight Training Handbook, Aviation Instructor's Handbook, Pilot's Handbook of Aeronautical Knowledge, Aviation Weather, and Aviation Weather Services.
Hope that helps. Good luck with your practical.