What item bonuses apply to my follower?
For example, Scoundrel has an item that has a magic property : "Monsters killed grant +9 experience"
Does he gains the experience for himself or it is the experience that i get? or both?
Yes , items the a companion has on him IE. +exp will benefit yourself aswell as them.
Yes, for the both of you: the full exp bonus for your follower, and +20% of that bonus for you.1