I think what you are really asking is, how, inside your task listener, can you "generate" the content links to the documents stored in the process instance. I imagine as part of your delegate service you are saving these URL's for another system, or something like that.
If this is the case, then what you really need is to recover the content ID's for the attached files as this is the only variable in the enterprise API to retrieve raw content.
The content ID for all documents associated with the process instance can be retrieved using the following REST API:
Alfresco Activiti - Enterprise REST Content
If you are looking for the Java equivalent you would use the RelatedContentService.
Check out the following forum post on how to use the RelatedContentService: