How can I tell if my Nissan titan is locking or non locking differential

See below, hope that helps. ELECTRONIC LOCKING REAR DIFFERENTIAL (E-Lock) SYSTEM (if so equipped) The E-Lock system can provide additional traction and should only be used when a vehicle has become or is becoming stuck. This system operates by electronically “locking” the two rear drive wheels together, allowing them to turn at the same speed. The system is used when it is not possible to free a stuck vehicle even when using the 4LO position (4 wheel drive vehicles). When added traction is required, activate the E-Lock system by pushing the switch ON. See “Electronic Locking Rear Differential (E-Lock) system switch” in the “Instruments and Controls” section. Once the system fully engages, the indicator light in the instrument panel will remain ON. When the system is activated, both rear wheels will engage, providing added traction. The rear wheels may momentarily slip or move to engage the system, and the system will only function up to approximately 4 MPH (7 km/h). Once the vehicle is free, the system should be turned OFF and driving resumed. The Anti-Lock Brake (ABS) system is disabled and the ABS light illuminates when the E-Lock system is ON. Also, the Vehicle Dynamic Control (VDC) system is disabled and the VDC light illuminates when the E-Lock system is ON.

Will it matter if i get a transmisson that for a locking differential and it's a non locking rear differentials. Truck

The locking differential is for the front, not the rear. The rear is an open differential. I have a 2011 Titan Pro-4X with the option. It can only be activated in 4x4 Low. Press the button and it locks the front. if you want a LSD (Limited Slip Differential) or an Air Locker, you need to get TruTrac for an LSD which can be around $500+ or an ARB Air Locker for $1000

Sorry Jesse, but you are completely wrong. The diff locker is absolutely for the rear diff, not at all for the front. That's why the switch shows an "x" on the rear differential. Not that you'll see this but maybe this will help stop some misinformation for future viewers. I am surprised there are no moderators on this site to at least spot review and correct this. I am also concerned about the 2 people who found your false statement helpful.

Exactly for rear diff.not the front.

So only on the pro 4x thanks

Turn the traction control off push the brake and gas in drive see if it leaves one or 2 black marks lol