Where would you put a level on the x5 to see if the transmission is level for filling
 

My drive way is not level but i have a number of floor jacks.

I would think a level on the door jamb would suffice

Drive your car onto level ground (like a parking lot), and then find your measurement spot. Then repeat when you're back in the driveway making it level. That's what I've done, actually using a magnetic level, shims, and tape.

I expect professionals do the ATF level check when the vehicle is on a lift, so the 4 lift points define what "level" is.

When I did my trans flush I put the level on the running board

Right across the bottom of the pan. No need to overcomplicate things.

Yup. Second. Level on pan. The pan is the dipstick. Meant so that you don't overfill or underfill.