i want to correct your mistake for this sentance.
"I hope you doing fine."
I think that it should be, "I hope that you're doing fine."
This sentance means that the person who said this hope that the one who is hearing feels alright.
"I hope you doing fine."
I think that it means "I hope that you are doing fine."
It is when you haven't seen someone for some time and you want to know how they are feeling. It is a kind of greeting.