P0136 - Bank1 Sensor2 is the rear O2 sensor located behind the catalytic converter. This is the O2 sensor you need to replace. See below:
This is a Paysite
Yes, Autozone was incorrect. What I provide you is out of Nissan service manual.
Here is a diagram showing locations of Bank1 Sensor1 and Bank2 Sensor1:
For every vehicle this is how to tell which O2 sensor is being referred to.
Bank1 is side where cylinder #1 is located
Bank2 is side where cylinder #2 is located
Sensor1 is before the catalytic converter(upstream)
Sensor2 is after the catalytic converter(downstream)