Yup, it is possible - got the answer thanks to this post: Application started in shell automatically "always on top" / Desktop / Xfce Forums; one can use
wmctrl for that.
First, in terminal, use
wmctrl to obtain a listing of currently active windows:
$ wmctrl -l
0x01a00003 -1 mypc Bottom Expanded Edge Panel
0x01a00036 -1 mypc Top Expanded Edge Panel
0x01200023 -1 mypc x-nautilus-desktop
0x042000e1 1 mypc Mozilla Firefox
0x03400024 0 mypc Terminal
0x032000f2 -1 mypc 2013-03-29
The "2013-03-29" is the title of my
stickynotes note window; then one can just run this command, in order to force that particular note window to stay on top:
wmctrl -i -r 0x032000f2 -b toggle,above
Note the use of
-i switch, to "Interpret window arguments (<WIN>) as a numeric value rather than a string name for the window.". Also, this toggles the "always on top" property for the window; so if you'd like to turn the "always on top" off - simply run the same above command again.
Note that if
stickynotes is set up to "Put notes on all workspaces"; then the "always on top" setting will be valid for all workspaces (although you may have to click through other windows at first, to have the window "understand" it should be "always on top").