I'm not 100% sure what you are asking... by default, JBPM does not actually use a database, not even an in memory one... but if you have set it up to use one, then you can access it in the normal ways... does that help?
I will give you the most basic solution. Use the connection properties from your persistence.xml and create a jdbc- java.sql.connection/ metadata to see the tables, data.
Or else migrate to a diff database. Dunno how to see the h2 db.