Check for the extension to be installed, please check the apt-cache policy Andrea gave. However, extensions being part of a mode don’t appear in the enabled-extensions list, which are additional extensions to the mode default (which has ubuntu-dock and ubuntu-appindicator for our case). If you are in the ubuntu session, you are running it if installed.
Edit: however, as Andrea told me, it’s still interesting to know if other extensions are potentially running and conflicting with it, so please report that command as well 
