There is NO direct bus from Palermo to Monreale.
First go to Palermo central station ..at the booth OUTSIDE the station.
Buy your ticket.
Wait for bus number 109 or 318 to P,zza Independenza.
There you will be at the Palace site and a bus stop on the Palace sidewalk.
Wait for bus number 389 this bus will take you all the way to Monreale..
Where the most beautiful church is waiting for your enjoyment.