Please use correct forum to post your questions. this forum is for questions/doubts pertaining to programmer exam i.e. SCJP/OCPJP.
but since i myself is preparing for OCEWCD 6, i would like to tell you there is no book available for Java EE 6 WCD exam. recently a book has been published by charles lyons(whose earlier book was sun certified web component companion 5 ) which targets the latest exam. have heard that book is good but this book is not yet available in india. you can check it on amazon site.
for more information you can dig in Web Component certification forum at http://www.coderanch.com/forums/f-18/java-Web-Component-SCWCD also browse through certification result forums and read success stories of people who have actually cleared the exam and follow their footsteps. many ranchers have cleared the exam using just the head firs servlet and jsp 2nd edition( this book is for version 5 exam) and reading servlet 3.0 specifications and learning extra topics by digging on the internet.
subject: Oracle Certified Expert (OCE) - Java EE 6 Web Component Developer