Other members with the premium pack have never found a 4pin trailer harness on thier vehicles... so far. If it was anywhere, it would be either under the rear bumper or in the spare tire area. Member jellsberg got her Rogue with the hitch and harness completely installed. The 4pin connector is to the left the hitch:
zerothread/323317
The rest of likely need Nissan's trailer harness (part no: 999T8-GU000) that consists of some connectors and the trailer harness to the tune of $150 USD.
As for non-premium pack model, I have first hand experience as I tore into it today to install my trailer wiring. There is a 2 pin power connector on the left side of the cargo area... underneath the bin that stores the tow hook (you need to unbolt and remove the bin). It's a constant 12V source for accessory power.
There is a cheaper option than Nissan's harness. I used the accessory power above to power a DrawTite trailer wiring converter (part #119175). The converter isolates the trailer lighting with relays so it won't blow any fuses and it converts the signals to the standard 4 wire trailer wiring harness. Armed with Nissan's trailer wiring insructions (Nissan Service Bulletin NTB04-049e), I then tapped into the existing wiring for the tailights. Being a bit anal, l also soldered all of my connections and carefully wrapped them with electrical tape. I then routed the trailer harness into the bin that stores tow hook by drilling a 1" hole though the side of the bin itself. This way I can coil the harness and hide it when not needed. The install took about an hour and the converter is about $25USD. I will be posting a step-by-step FAQ at some point.