I was told my son's ekg has a slight st elevation with repolarization. he is 11 years old an an extremely active athlete. should he stop hockey?

Probably not: It sounds like you're referring to normal variant ekg finding, common in young males, called "early repolarization." there's no evidence firmly linking this with future cardiac risk. If your son has had absolutely no symptoms with sports (i assume not), may not need anything more. If any concern, or ekg not convincingly benign to the doctor, an echo will rule-out structural heart disease.

Temporarily stop: Questions for you would be: does he have chest pain, did he faint during exercise, why did he have the ekg to begin with? Your son should definitely be checked out by a cardiologist. Usually i would send to a sports cardiologist and have them do a 48-72 hour holter monitor, echo, stress echo/ stress test to make sure we aren't looking at any time of cardiac issue that can cause sudden death.