Elios, Loyal Dragoon

Q. If I attack a 0-attack enemy follower with this follower, do I still give this follower and my leader +1 defense?

A. No. When a follower with 0 or less attack deals attack or combat damage, it doesn't count as dealing damage.

Q. If this follower takes damage that brings it to 0 defense or less during my turn, do I still give this follower and my leader +1 defense?

A. Taking damage triggers this follower's automatic ability, but by the time you resolve it, this follower has already been destroyed and put into the cemetery, so while you can't give it +1 defense, you do give your leader +1 defense.