Like everything Amtrak, they do things differently at Lorton than they do at Sanford. In Lorton the little booth where you check your car in will have an Auto Train ticket folder already prepared with a label with your name on it. You just drive up to the booth and provide your name, they assign you car a number and write that on the folder, and then direct you to a lane to turn over your car.
In Sanford you provide your name, they check a list of expected arrivals, write your name on a folder along with the number assigned to your car.
Either way, after you drop off the car, you proceed inside for the checkin. Again you just provide your name, show a photo ID, and then select your dinner time. They'll also assign you a seat & car number and write that in your folder.
No actual tickets will be printed or needed, unless you used AGR points for your reservation.