[PJ-Comix]

Superman was raised as a Methodist by the Kents; I'm not sure if he still attends.

That was just a cover story. Superman was actually Jewish but had to pretend to be Methodist since they were unable to circumcise him.

[B-Chan]

That angle was covered in Superboy Special #8 (August 1949), in the story "Superboy — Super Catechumen!" In it, we see (via a flashback) a young Superboy (as Superbaby) in the process of baptism, circumcising himself by bouncing his heat vision off a metal offering plate. The subject matter was considered daring at the time.