Where is the toilet smoke detection indication displayed for a B777-200/300?
From the 777 manual:


  Each lavatory has a single smoke detector. If smoke is detected, an aural alert
  sounds in the lavatory and in the cabin. In addition, the lavatory call light
  flashes and the master call light at the associated attendant station illuminates.
  The EICAS advisory message SMOKE LAVATORY indicates smoke is detected in
  one of the lavatories.


The EICAS is a display in the cockpit.

It is treated as a fire, and the cabin and flight crews follow the set procedures to handle it.