Answer
We do not get Power Takeoff (PTO) switch state from the engine on J1939. We get the PTO governor state. You may try tweak the governor state values we use for PTO on/off using the following custom parameter, but it is not guaranteed to work:
<GoParameters><Parameter Description="Use PTO Governor Hold And Standby As Active and Use J1708 Switch State As Active" Offset="36" Bytes="04"/></GoParameters>
The only reliable way to get PTO state may be with an AUX.