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