This works for me on Lubuntu 18.04:
<keybind key="C-W-C"> # my vlc
<command>sh -c 'vlc -vvv "$(xclip -o)"'</command>
Remember to run
openbox --reconfigure after saving your edits to lubuntu-rc.xml.
If you have any output from
openbox --reconfigure, you'll need to fix the issues mentioned.
Edit: You normally1 can't have shortcuts with two non-modifier keys. Common modifier keys are C (for Control), A (for Alt), S (for Shift) and W (for Windows aka Super).
1 See https://web.archive.org/web/20190815101235/http://openbox.org/wiki/Help:Bindings for more:
KEY-COMBINATION is the key combination which you want to bind to the
actions. The format for the KEY-COMBINATION is: Modifier-Modifier-Key.
Any number of modifiers (0 or more) can be used together, and they are
each separated by a "-". Multiple KEY-COMBINATION can be specified in
one keybind by separating them with spaces. This is useful if you use
multiple keybinds for a thing that is quite complicated to specify.