Developers should be able to google.
Everything else can be learned from there.
But seriously: look around at some news pages and job portals and just look around. You'll get a pretty good view over what's important.
Some of the J2EE basics are almost always usefull: JDBC, Servlets, JSP. Others are required sometimes: EJB.
Tomcat Know-How is a definite advantage, as is Spring and Hibernate.
Basically I'd say that for most jobs server-side Java is the most important part.