Hey Mike,
according to Confirmed Aftermarket Screens/Monitors that work with the Onefinity, Asus VT229H works.
You could open a terminal window with Ctrl-T Ctrl-C and type:
sudo grep -i touch /var/log/Xorg.0.log
If a touch device was found, it would be shown. Otherwise this command would output nothing.
Next, what happens if you type:
sudo tail -F /var/log/syslog
and then you plug the USB cable in?