The current owner's manual posted by Escape
says "place the jack under the axle mounting bracket", and provides an illustration on page 17. Unfortunately, this means jacking ahead of the axle line, so it is not as stable as jacking behind the axle line, and it's hard to reach there because the wheel is in the way. If you have a jack with a cup or rubber pad which will hold the bottom of the frame securely, my suggestion of an alternative would be on the frame behind the wheel, as close to the wheel as you can reasonably get your jack.
One problem unique to the fifth-wheel trailers (5.0 and 5.0TA) is that they have two front jacks, so if you jack up one side of the trailer when it is not hitched to the truck you will be twisting the trailer frame and body. That's not a problem if supported by a single point at the front (the hitch), so it would be better for the trailer to jack it up while still attached to the truck and not using the front "landing gear" jacks - that would be the case anyway, if you're only jacking it up to change out a flat tire on the side of the road.