Thanks again Krytarik and stinkeye. With these commands, I managed to write a little script that shows the time in a notification box, disabling the fullscreen of mypaint which usually runs as a notepad on my tablet's screen blocking the notifications:
Not quite perefect, since it does not hide the menu, as it does when I press F11. Don't think wmctrl can acess this property though..
date_time="`date | cut -d' ' -f1,2,3,4`"
wmctrl -r MyPaint -b remove,fullscreen
wmctrl -r MyPaint -b add,fullscreen
Also I added "wmctrl -r :ACTIVE: -b toggle,maximized_vert,maximized_horz" and "wmctrl -r :ACTIVE: -b toggle,fullscreen" to easystroke gestures