If you want to know all of your weights;
1. Weigh the truck without the trailer, both axles on the scale.
2. Pull forward until the front axle is off the scale to get the rear axle weight.
3. Subtract the rear axle weight from the combined weight to get the front axle weight.
4. Hook up the trailer and go back to the scale.
5. Pull the front wheels of the truck onto the scale and get that weight.
6. Pull forward until the rear wheels of the truck are on the scale and get that weight.
7. Pull forward again until the front axle of the trailer is on the scale and get that weight.
8. Pull forward again until all axles of truck and trailer are the scale and get that weight.
To get the pin weight subtract #1 from #6.
To get the combined weight of the trailer axles subtract #6 from #8.
To get only the front trailer axle weight subtract #6 from #7.
To get only the rear trailer axle weight #7 from #8.
I know this sounds complicated, but it really isn't.
Edit -
We must have been answering at the same time Phil, you beat me to the draw.