I bought a QX4 a few months ago and the receiver dryer had a hole in it. I imagine the system had been empty for a while, but I just swapped in a junk yard dryer and filled it up w/ a can of AutoZone synthetic R134a. My FSM (Factory Service Manual) calls for "type s" oil... but I never found any cans that actually said what type of oil it has. IMO, virtually all common R134a systems can take any can of R134a.
Just buy a can that has a moisture control / remover and oil, and fill it up. Just make sure you check the gauge and don't over fill.
Also, download your year's FSM:
http://www.nicoclub.com/FSM/Pathfinder/
EDIT...
Also, if you plan on changing the oil, I assume you have a vacuum and manifold / gauge set?