Xfce by default does not open the Application Menu nor the Whisker menu when the Win Key or Super Key is pressed. It requies manual setup. Follow these steps to set Win/Super Key as the shortcut for Xfce Application Menu or Whisker Menu
Launch Settings Manager
Go to Keyboard
Open the Application Shortcuts tab
Press Add
**Command for Xfce Application Menu **
xfce4-popup-applicationsmenu
[attachment=1]xfce-application-menu-command.png[/attachment]
Command for Whisker Menu
xfce4-popup-whiskermenu
[attachment=0]xfce-whisker-menu-command.png[/attachment]
Press the OK button
Now press the Win/Super key