which NOX sensor do I change

If you're asking about bank 1 and is it a location - you need technical assistance to properly diagnose and repair this vehicle. The "OBD Reader" does not diagnose the vehicle. "Issue with the NOX sensor bank 1" could be a wiring concern or a concern where it's reading improperly due to influence from another component. No code means "change this sensor". Seek professional guidance before wasting your money at a parts store for something you don't need. www.repairpal.com/repair-shops