It depends which exam you're insterested to take. The current SCBCD exam (CX-310-091) is about
EJB 3.0 and JPA 1.0. EJB3 In Action is a great book to learn about these. Oracle has decided to split both EJB and JPA into two different certifications :
CX-311-093 and
CX-311-094. These are respectively about EJB3.1 and JPA2.0. They are in Beta phase and are already closed. I don't know when the new exams will be officially published.