It can be hard to find, but here it is, The Washington State Home Inspector Handbook.
It will Give you a great idea what you need to know so you can set your inspection license. It covers the test subject matter and gives you the breakdown of how each section is graded.
Washington State Home Inspection Candidate Handbook – This handbook provides information that you will need to register for the Home Inspector Examination for Washington. Be sure to keep this handbook after you have registered for the examination; you may wish to refer to it later.