You can also visit the homepage of your PPF manufacturer for this info. For example, if you visit Xpel's FAQ page, this is what they say in answer to your question (see below). You should install PPF first and then install the ceramic coating on top of the PPF. If a coating has already been installed, it is best to polish it off, apply the PPF, and then reapply the coating on top of the PPF.
From
XPEL | Help | Frequently Asked Questions :
Can I Have XPEL Paint Protection Film Installed On Top Of My Ceramic Coating?
We would not recommend this, as it may result in poor adhesion to the painted surfaces. Professional removal of the ceramic coating is recommended. You may install XPEL FUSION PLUS on top of your XPEL Paint Protection Film. Check with your local installer for more details.
(Fusion Plus is Xpel's own brand of ceramic coating)