p36nfo69 substrate pin
The tab ties to the drain of the device, same as pin 2.

There is no separate substrate connection for this FET. The substrate (body) is internally tied to the source to ensure the body is correctly biased. That's the reason for the body diode in the diagram. More about that here: How should I understand the intrinsic body diode inside a MOSFET?

There are FETs with separate body connections, allowing the user to control the characteristics of the FET, but this isn't the norm for power FETs like the one you show.