Hi, basically you have two different things to solve, one is about how to locate the correspondant session and the other is how to choose the right process to notify the event right?
For locating the right process to signal and to restore the right session we usualy implement a business layer that store a business key and information about your workitem or processid.
Take a look at the following example, using that layer you can also map a JMS message to a specific event or workitem to complete. I think that you can use the same approach provided in the example.
Example: https://github.com/Salaboy/Drools_jBPM5-Training-Examples/tree/master/jbpm5/03-jBPM5-SimpleEmergencyServiceProcessAsyncWorkItemsExamples
Hope it helps!