I've looked in the manual because I know they changed the method of filling and checking the transmission fluid ... and everything I can see says yours should be the "new" way.
There are two plugs: one under, which is the drain plug, and one on the side (or also underneath, but with a deep section to it), which is the overflow plug. You drain the ATF using the drain plug then fill it by pumping fresh ATF into the overflow plug until it starts to overflow. The gearbox is then full.
They're supposed to last "the life of the vehicle" but in real terms you could change it more frequently (haha!) and it won't hurt, as long as you use the right fluid. Automatic transmission valving is quite dependent on the correct grade of oil being used, so you need to find one that matches - Penrite etc should have a chart and I'd rely on that, but you could ring a dealer and ask them how much they charge for "Genuine Nissan" oil specific to your gearbox. If it's the 5-speed it needs either Nissan Matic S ATF but can also use Nissan Matic J ATF. If it's the 7-speed box, the manual only mentions Nissan Matic S ATF.
Filling it is a PITA. Nissan in their infinite wisdom decided to make it very difficult for the home mechanic to do, and it requires a pump to push the fluid up into the gearbox.
There's some good info on filling it in this thread, including a recommendation for a pump.
https://www.navaraforum.com/threads/d40-2008-auto-issue.38196/
