This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Web service can be implemented using EJBs and will then have certain characteristics. Thus knowledge of EJBs are beneficial when preparing for SCDJWS.
Working experience of web services is not necessary, but perhaps a lack of it will cause you to spend more time studying.