You have to install first the drivers for TPU Coral, more info here: Coral gasket dkms drivers.
After installing drivers you’ll have the /dev/apex_0 device then you can map as “Host Device” and “Container Device” as /dev/apex_0 and hopefully TPU should work.
Keep in mind: You’ll have to use dev-mode, the drivers will be removed after a Truenas Scale update, you’ll have to reinstall again and it’s not officially approved method.