How does one get from Geneva Cornavin rail station to Hermance?
You can get timetables from www.sbb.ch/en.
Looks like you have to take tram number 16 from the station to Rive, then a bus to Hermance. Three or four connections per hour.
Bus 5 towards Thonex, get off at Rive and walk 3 min to take Bus E to Hermance