I'm going to feed my dad's dog [legal] cbd dog treats without him knowing
Is there a reason you want to feed the dog CBD treats?
Nope, I just want to see what happens.
People's pets are their responsibility so it's expected that you ask their owner's permission before feeding them something they normally wouldn't. Their pet may have an allergy or condition unknown to you and if you feed it something harmful you'd be at fault.
I'm being safe. I put the treats in a nice bag, taped it and wrote "cbd dog treats" on the bag.
Writing on the bag may warn people, but that doesn't make it safe for the dog. The dog doesn't belong to you, so you should respect your father and inform him before giving his dog any food.