How to use the AEM listeners for the workflow completion.

https://helpx.adobe.com/experience-manager/kb/CatchAndProcessWorkflowEvents.html 

Have you checked that link? it shows an example of listening to workflow events.

Few options:

1. Events in AEM works on a change / modification in node or property [1], now If youe first workflow does any of these, then it will automatically trigger event listener. Inside event listener you can call Workflow process

[1] http://blogs.adobe.com/experiencedelivers/experience-management/event_handling_incq/

[2] https://helpx.adobe.com/experience-manager/using/events.html

[OR]

2. Based in property or node change done by first workflow you can create a workflow launcher which will call another workflow  (would be simple and configurable)

3. Add a step in the end of Dam Asset Workflow which will executes another process step

Thanks

Hi 

Adding a reference article covering "Listening a workflow event ":

Link:- https://docs.adobe.com/docs/en/aem/6-0/develop/extending/workflows/wf-extending.html#Listening for Workflow Events

I hope this would be of some help to you.

Thanks and Regards

Kautuk Sahni