This may not be correct but it is all I could find.
Determine the sex of your Jackson's chameleon from the age of three months, which is when the chameleon reaches puberty.
Pay attention to the chameleons head, as this is where you will find the physical characteristics that display the gender. Look for two horns spouting from just above the eyes on the merumontanus Jackson's. The male will have noticeable horns, whereas the female's horns will be diminished or nonexistent.
Look for two large horns, one in front of the other on the head of your xamtholophus Jackson's chameleon. Large horns indicate that the chameleon is male, whereas a small bump indicates it is a female