You can also go to a Truck Stop with CAT Scale and take readings. For a small extra charge, you can take 2 readings. The first reading is with both truck and trailer. Truck is positioned on one scale and trailer on the other so there is a separate weight for each. Then pull off the scales, go back to the parking lot next to the scale and unhitch. Then weigh the truck. The difference in truck weight between the two weighings is your pin weight. The difference between the sum of truck and trailer, and truck alone, is your trailer Gross Vehicle Weight.
On ours, the first reading might be 13,500 for the truck and 12,500 for trailer. The second would be 10,000 for the truck. 13,500 (loaded truck) - 10,000 (unloaded truck) = 3,500 pin weight. 13,500 (loaded truck) + 12,500 (trailer axle weight) = 26,000 for combined weight, less 10,000 truck weight = 16,000 trailer GVW.
Last time we weighed, our actual pin weight was 3,700 vs a factory spec of 2,620.