In the United States
There are two main requirements to become a hockey referee.
#1: Register with USA Hockey and take your online open book exam.
#2: Register for a seminar with your local affiliate. Depending on your state you will need to find your local affiliate and sign up for an in person seminar.
After completing your open book exam and seminar you will become a registered official. You can find more information on obtaining game assignments from your local affiliate where you registered for your seminar.
USA Hockey Officiating Program Home Page
Registration opens August 1st every season.