Have someone take you to a CAT scale. First pull on and get the ticket showing the weight on the trucks front axle, back axle, and trailer. CATs have 3 weigh points so you'll get those three on one pull thru. Now pull around and drop the trailer off in the parking lot. Pull on the scales a second time to get the trucks weight. Each weigh ticket will show total weight all axles. The diff between the two tickets total weight is the trailer weight. The diff between the sum of the truck axles with trailer attached vs. the sum of the truck axles no trailer represents the trailers tongue weight.