You can either print it from one of the Kiosk machines or go to the ticket counter and they can help you print one.
It depends on if you have an annual pass or just a day pass if you have an annual pass you can do what Jack said or if you have a day pass AND you are still in the park your not going to be able to get back in if you walk out you will have to buy a new day pass. So a good note to make is to NOT lose your pass.
Thanks! Your answer is awaiting moderation.