Java 9 was released but it hasn't came yet for the Oracle Exam not even Beta exam, so at this point of time there is no path from Java 6- Java 9 but ya there is a path from Java 6-Java 8. I think you are talking about this exam->
Hava a look at this page. I think you are talking about this exam. So there is no direct book for this exam(i guess because there are no books on Amazon) but you have to study from the Java SE 8 by Jeanne Boyarsky which is available on Amazon(before buying first see that your contents are matching or not)