It sounds to me like you're looking for files uploaded by a given asset. Assuming I am correct this feature is not available through the 6.8.x line using the v2 sdk. You will need to use the v1 sdk (UploadedFileFinder) to access uploaded files.
We have an ongoing effort to unify the "File" experience in the Axeda 6 Platform and in 6.6 FileInfo objects are used for generic "file" access and they are also possible to be used/reused as part of download instructions in the software package download features of the platform. In 6.7/6.8 we added support for FileInfo in ExtendedApplication objects.
I believe that agent uploaded files is something the product team is considering supporting in the future however as I am not in the product team, maybe this would be better put towards them. I don't know what the usual channels are to try to encourage development in any given direction - perhaps a call to the support team?
Hope that at least answers the question (if not 'help')