Place the persistence.xml in the META-INF inside each EJB jar file.
Also you can uyse tag to point to specific jars holding entities.
according to section 8.2 JPA specification:
Within Java EE environments, an EJB-JAR, WAR, EAR, or application
client JAR can define a persistence unit. Any number of persistence
units may be defined within these scopes. A persistence unit may be
packaged within one or more jar files contained within a WAR or EAR,
as a set of classes within an EJB-JAR file or in the WAR classes
directory, or as a combination of these as defined below. A
persistence unit is defined by a persistence.xml file. The jar file or
directory whose META-INF directory contains the persistence.xml file
is termed the root of the persistence unit. In Java EE environments,
the root of a persistence unit must be one of the following:
- an EJB-JAR file
- the WEB-INF/classes directory of a WAR file[80]
- a jar file in the WEB-INF/lib directory of a WAR file
- a jar file in the EAR library directory
- an application client jar file It is not
required that an EJB-JAR or WAR file containing a persistence unit be
packaged in an EAR unless the persistence unit contains persistence
classes in addition to those contained within the EJB-JAR or WAR. See
Section 8.2.1.6.