Who we can call owner of the AI generated content? Owner of the tool of User of the tool?

It depends ... the tool user inserts a prompt and receives a generated answer, so the Owner of the tool owns answer data, while the user is the owner of the prompt data. If the AI was a simple processor, which means it gets a prompt and returns the same prompt then the user would be the sole owner of the data returned. Of course, this could change, where you could create a form of contract that gives the owner of the return-generated data to the user who prompting it, but it's not the case for any top AI generators right now.