1.
Do you know of this guy?
I think that the sentence above sounds a little unusual to me.
I would ask.:
Do you know that guy
meaning do you know who he is (in this context this doesn't mean that I am asking if you personally know him ).
The phrasal verb
know of = I have heard of the person before (briefly) and don't know much about the person.
Know of is used a lot with pronouns,and improper nouns. lOOK AT THE REPLIES BELOW.
Have you heard of Donald Trump? I know of him.
Have you heard of the Jones? I know of them. They live down the street.
I am having problems with my car. I know of a good mechanic who can fix your car.
I have a pain in my leg. I know of a great doctor who will heal you.
2.
I know a little about Morgan Freeman, he is an Oscar winner.
Yes, this sounds good.
know about here is stating that you know something about morgan Freeman (what he is, what he does etc).