J2EE itself contains lots of stuff. it actually contains a whole lots of Java technology. how about all XML related topics, SOAP, well EJBs of course, JSP topics such as custom tags, servlets, web services, and so on. I recommend you to go through J2EE tutorial that will give you all you need to know.

but the most important  fact in J2EE is how you design and develop you I encourage you to have a look at J2EE design patterns too as you go.

start with java.sun.com

BTW, join www.javapassion.com to learn J2EE in online class, It's free.