How to stop run the screenkey
You can exit from Screenkey by right-clicking on its status icon and selecting "Quit":
If you're using GNOME/Unity and cannot see any status icon please make sure the python-appindicator package is installed. Run the following inside a terminal to install as required:
sudo apt install python-appindicator
On any other desktop system Screenkey uses the regular system tray. If you don't have a systray or you cannot quit an existing Screenkey, use the following command in a terminal to kill it:
pkill -f screenkey