My son has dry skin on his penis and other parts of his body. I got the one on his eye and behind his ears to go away. But his penis will not. Help?

Eczema. Your description sounds like eczema but it could be many other issues and need to be evaluated by a dermatologist.
Dry skin. Your son may have an infection or other condition that requires special treatment. Make an appointment to see your pediatrician concerning this problem.