My dad has mono(test conf) -no symp. he's with my 2yo abt 2hrs, 2x a week. no food/utensil sharing but close interaction. how likely is son to have it?

Little risk: Infectious mono is rare beyond age 20-25. However, assuming your dad's diagnosis is correct, it's not so easily transmissible -- usually by sex or intimate kissing. He should use common sense hygiene and avoid directly exposing your son to his saliva. But normal child-grandfather interactions pose little if any risk. (Your child is at much higher risk of this virus from kids in day care etc.)