Hi Rahul, I am also preparing for the same.
I guess if you have good experience in the J2EE technologies, a high level understanding is enough.
From what I understood from this forum, this is not a code level exam. Most mock questions I have seen are scenario based.
A brush up of JSP / Servlets, JSF, EJB 3, JPA 1, JMS, SOAP / WSDl / JAX-WS / JAXP / JAXB / REST etc would be good enough (high level)
SCEA/OCMJEA tests your concepts and not literal syntax. In my part1 - i got 1/2 questions regarding syntax also. Generally i have found candidates who are from grounds up fair better in SCEA. I will always recommend at least go thru JEE tutorial once.
For SCEA, excuse me OCMJEA, I do not recall a single question that contained syntax. They do ask questions about declarative security versus programmative security (in the deployment descriptor vs. coded into the EJB itself), but not about the syntax.
I think what's especially important is to know things like (a) why to use REST instead of Web Services or RMI, or why straight JDBC over CMP (container managed persistence). If you think JDBC is better, use that if you have decent arguments for it. And (b) you should know to pick one of the right technologies or a good solution, when confronted with a given requirement. If the requirements ask for scalability, then doing everything with servlets is probably not a good idea.