The first one is correct and used often.

"Who has written this book?" is grammatically correct, there are a couple of options that sound slightly more natural to me: Who wrote this book? Who is the author of this book? "Is this book was written by?" needs to become - Was this book written by John Smith? - we need the name at the end for the sentence to make sense and because we're using "written", which is in the past tense, we need to say "was", not "is"

Both are bad. You can try saying, "Who is the author of this book?" or "Who wrote this book?"

Both.

You can ask "What did you say about who wrote this book?" if you are asking someone to tell you facts about the writer NOT who the writer is. Otherwise it would be "Who did you say wrote this book?"