From the airport :

Bus no. 59: Direction "CHAMBESY, PLAGE VENGERON". Departures every 30 minutes, journey time 10 minutes. Get off at the 5th stop "GRAND SACONNEX, JOHN KNOX", located in our parking lot.

From Geneva-Cornavin station:

Bus no. F : Direction "FERNEY-MAIRIE" approx. 11-minute journey - 7 intermediate stops - departure every 5-7 min.

Get off at the "OMS" bus stop, then walk for about 10 minutes.
From the bus stop, continue on Chemin des Morillons towards Avenue Appia, then before the crossroads turn left onto Chemin de la Riole. Follow the path up to the chapel, then turn right onto Chemin des Crêts-de-Pregny and follow the road to the center.

Bus no. 8 : Direction "OMS" approx. 13-minute journey - 9 intermediate stops - departure every 6 minutes.
! Please note! The "OMS" stop is not served on Saturdays and Sundays. Stop Appia. 

Get off at the "OMS" bus stop, then walk for about 10 minutes.
From the bus stop, continue on Chemin des Morillons towards Avenue Appia, then before the crossroads turn left onto Chemin de la Riole. Follow the path up to the chapel, then turn right onto Chemin des Crêts-de-Pregny and follow the road to the center.