Adding to the above comments, As you said for a Java developer its important to know basic concept on webloigc/websphere like :
1) How to Create and Start/Stop the Server Instances.
2) How to depoly the Applications at Server Instances ( EJB/EAR/JAR/WAR.....).
3) What is Cluster?
4) How to make JDBC connections(Connection Pool/DataSource).
5) Needs to understand the Hierarchy of the Deployment Structure of application.
If you want to know more on the weblogic , please refer http://download-llnw.oracle.com/docs/cd/E12840_01/wls/docs103/