Hi @OmahaOmaha,
Thank you for your question! Unfortunately, it isn't possible to display the document thumbnail on an issue level report using the native Workfront functionality.
If you haven't already, I would recommend submitting a feature idea to the innovation lab HERE. As a workaround, you could use a document report (where you can reference “thumbnail” through the UI) and customize it with text mode to reference the issue level data they want to see.
- Monica