You provide the transaction manager when creating the session. Something like:
Environment env = KnowledgeBaseFactory.newEnvironment();
env.set(EnvironmentName.ENTITY_MANAGER_FACTORY, emf);
env.set(EnvironmentName.TRANSACTION_MANAGER,
TransactionManagerServices.getTransactionManager());
final StatefulKnowledgeSession session = JPAKnowledgeService
.newStatefulKnowledgeSession(kbase, null, env);
Regards,
Demian