I have a hobbywing sensorless ESC I'm using in my slash, but I have a novak sensored motor in it. I noticed there was an empty hole and solder traces on the PCB for the socket the sensor wire goes into, so I figured I could add one.

Does anyone know what that plug is called, where to get one etc?
Thanks

Even if you were correct and could somehow add the connector, theres no firmware on the esc to make the sensors work correctly. For the risk of messing something up just order a brushlesshobbies esc for ~$60 and not worry about it.
With the cheap costs of so many esc's now a days theres just no sense trying to mess with that...

I believe the firmware would be there...it's the same ESC as the sensored version, this one is just the 'rtr version' and there's a hole in the case.
For me it would be worth it if I can buy a $2 plug and have it work...if it doesn't work, it won't hurt anything.

I solder stuff smaller than this regularly, so that wouldn't be an issue. Actually, if I could just get the pinout on this so I knew what order the wires went in I'll just solder the wires directly to try it.

What RTR vehicle did it come out of?

Sensor connector and wiring info, check out section 8.8 on page 50:

2010 ROAR Rule Book