Can anyone tell me where I would find help files/docuementation for the use of AGOL Assistant?
There is none. You should make a request for documentation on the git hub repo site:
GitHub - Esri/ago-assistant: A swiss army knife for your ArcGIS Online and Portal for ArcGIS accounts
If you have a specific question please post it.
Is this an ESRI owned product or open source?
ESRI Open source
I agree, the AGOL Assistant is great but its not supported by ESRI for official use... if they had documentation it would benefit the community greatly.
What are you looking to accomplish with AGOL assistant?
Retrieving data ...