Panatomic X on film was EI 25-EI 32 when new, so I would suggest try at EI8 as a starting pont for the panatomic X if old.
Process pan suggesta a graphic arts panatomic type film. I would try exposing it at EI6, since it is likely means for use in a process camera for copying colour materials.
If it is graphic arts oriented than DK-50 can work, as can Dektol 1:3 in a pinch, but then you will get gobs of grain. It would tell you if the stuff is fogged.
Try pulling from the middle of the pack for your first test, unless each is wrapped individually.
The emulsion face facing the wrapping can age differently than those against other film/photo paper/plates.