I have only tested it with the G923 Pedals but it should work with previous generations too (G920, G29, G27, etc) as long as they use a DB9 connector. You will need an arduino board of your own ...
The case has a slot for a DB9 plug (the side with the pins). Connect the DB9 plug to CAN_H and CAN_L of the CAN-hat; connect GND and 12V to the watchdog. Pinout is as follows: OBD2 DB9 4,5 GND 1,2 6 ...