Between the callback names and the 'skeleton' functions in CvGameUtils and CvEventManager I've found them to generally be very self-explanatory. Any time I am in doubt, I look into the SDK to see how it is called.
For example, If I wanted to know how USE_CANNOT_FOUND_CITY_CALLBACK was used, I'd search the SDK for GC.getUSE_CANNOT_FOUND_CITY_CALLBACK which would take me to CvPlayer::canFound() and show that if that callback is enabled, the Python function CvGameUtils.cannotFoundCity() is checked and if it returns 1/True then the player is not allowed to found a city on that plot.
Are there any in particular that you don't know about?