I would like this clarified....how can I sniff data on the canbus? I was expecting to be able to grab signals from the bus simply by plugging into my car and then doing things like indicators, brakes etc.

But so far I see nothing.

Same here with my Audi A5:
Started the link with "sudo ip link set can0 up type can bitrate 500000" and then started cansniffer, but nothing.
This page: https://jazdw.net/tp20 suggest that you have to open a channel by sending commands to a control unit.
But that also means that with VW/Audi/Skoda it is not possible to sniff on the gateway can. You can only talk to a specific device.

USB2CAN is only bridge between USB and CAN bus.Your software on PC side MUST know how to sent or get frames between PC and your car.
It does not know how to interpret the frames.Also it is NOT dedicated for cars diagnostic.

It's not a matter of the USB2CAN device. In VAG cars, the can bus is not directly connected to the OBD2 plug. There is an interface in between. From the OBD2 plug, you can talk to CAN devices and get the answer, but you cannot passivly listen on the bus.