need help..p0156 error code-o2 sensor bank2 sensor2

Hello, Need help. I have a 2001 4 runner v6, 2wd...I just got the dreaded engine light on. Both the trac lights came on also..Took it to Autozone and they provided me a p0156 malfunction code. they said it was a malfunctioning o2 sensor. It was the bank 2 sensor 2 one. Autozone couldn't tell me exactly where it was located. Questions..Is the sensor before or after the catalytic converter? Are there two sensors that I need to be replacing? Thank you for your time and help. J.Richards...