When using dual monitor and you wish to use the Displax Skin just with one monitor, in Ubuntu, you need to preform adicional steps (after completing configure the Displax Skin settings) in order to associate the Displax Skin to the monitor you desire the touch events will be injected.
Open a Terminal and execute the following steps:
1 - run the command "xinput --list"
This command will show you the connected devices. We need to pau attention to the ID of the Displax Skin
2 - run the command "xrandr",
This command will show the monitors connected on your computer.
3 - Run the command "xinput map-to-output ID MONITOR", to map the touchscreen to the monitor connected on the HDMI.
For example "xinput map-to-output 11 HMDI-1" where the ID = 11 (got it from the step 1) and MONITOR = HDMI-1 (got it from the step 2).
4 - As final step you should run this command every-time the computer reboots as Ubuntu may loose this configuration after reboot. You can put this command on the startup of Ubuntu.