I thought it triggers every time you get VPs. Which makes it quite powerful. If it does not trigger on all VP effects, we certainly need a complete list when it triggers and when not.
Where did it say that it does not trigger when killing enemy figures ?
It triggers every time you get VPs from techs, ruins, cities.
The only exception is the "ransom" VP you get killing an enemy figure if you already killed one figure of all your opponents.