To be completely honest, I do not really know which tables the attachments are kept. The good news is that it doesn't really matter. If you want to get access to the workflow attachments you can use Function Module SAP_WAPI_GET_ATTACHMENTS. This will return all the attachments of a work item.
The multi-line parameter attachments will have an instance(s) of SOFM. You can loop through those and display the created user ID and more.
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