This eBay listing has actual-item pics that show the locations:
http://www.ebay.com/itm/162186979801
You didn't specify which revolution sensor you want (there are two of them). The turbine revolution sensor is on the top of the bellhousing, slightly on the driver's side. The other revolution sensor is on top of the intermediate gearbox at the end of the transmission, before the transfer case. You should be able to see/feel the TRS from under the truck, but the RS will be out-of-sight.
I agree that sometimes the FSM locations aren't clear, but I disagree that this is one of those times:
http://www.nicoclub.com/manuals/QX4/200 ... ission.pdf
Page AT-12, lower left diagram. It's clear that the sensors are on top, and there are no other electrical components nearby that could be mistaken for them.