Hi Joonas,
You'll need a qube with the Network Manager service enabled - using a
proxy makes sense.
By default the applet is hidden - there's a script to govern this:
/usr/lib/qubes/show-hide-nm-applet.sh
Enable the service:
'qvm-service <qube> -e network-manager
Start the qube, and the nm-applet should appear in the panel.
unman