According to Config Notes you can find the upstart script at:
/etc/init/wiki.conf
See upstart script notes on site 
Here is our upstart script. Adding --admin ???? does not seem to work / make a difference with regard to plugin admin rights.
start on started networking stop on stopping networking respawn env PATH=/root/.nvm/versions/node/v6.11.3/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin env HOME='/root' exec wiki -f -p 80
# See also