I would suggest taking a look at this site:
http://www.oracle.com/technetwork/java/javaee/tech/index.html
As it's
JEE 6 web component exam, I assumed the JSP, JSTL and EL versions from the link above.
The spec was released a long ago but I don't think that there are many books purely about servlets at all. It's more like developing web application using Servlets and these books are great of course, but are not the best source of knowledge for the exam.
The exam itself was released in mid April 2011, so it's quite fresh. If you'll wait few weeks I'm sure Enthuware will release their SCWCD 6 mock exam soon.
Cheers