When you click on the "remind" option in a document approval, there doesn't appear to be anything that is logged to say "a reminder was sent on X date at X time". Or even to confirm a reminder has actually been sent at all (ie something coming up to say "reminder sent".
If you sent a status update to someone giving them a nudge, you'd be able to see that you'd had to chase them and when, but there doesn't appear to be anything to show this in WF in the document details section.
