Google dot com or Ask dot com and enter the name of your trailer's manufacturer.
Thouroughly inspect the vehicle for a placard or sticker which should contain the Make/Model/Year of Manufacture and other information, much as you would find in the door frame of your car or truck....
one hot tip is go on craigslist.com Then enter your area. Then there proberly is some cheap deals.
If it is just the screen that is damaged, your local glass shop can replace it.
It should be stamped on the hitch but it may be covered with someones paint job. It could be 1 7/8", 2" or 2 5/16".