How Kubernetes Pulls Image from outer respository? Where is the image stored?
Who is downloading the image from dockerhub?
The Kubernetes itself doesn't pull anything. Images are downloading via runtime'a client, e.g Docker
When a the image is pulled, is it stored in any local folder in kubernetes?
Again, it is the runtime's task. Depending on the runtime and its configuration it might be different. In case of Docker it will be like it described in @Praveen Sripati's link