Is it possible within a Workflow to loop thru all items in a list and determine if an attachment has been modified ? My goal is to send out an email if someone modified an attachment, but I do not want to send out an email if the list properties have been modified (any column other than Atttachment)...
Currently there's no Nintex feature or information to do this. I think that not even could do it with a SharePoint feature or information.
You could write some code so as to get information from attachment ( See Files and folders REST API reference ) but I think it is not enough because you'd need to make some comparisons with item Modified column and the property TimeLastModified of the attached file. It's a hard work.
you could consider storing of files in document library instead of attaching them to list items.
in document library you would be able to trigger a workflow on document upload or change events.