Is there a way in CORE to see what fields were corrected and resubmitted on a document that was rejected?

There isn't a way to see changes made to a document. There is a Document History Query the allows you to see information on the history of a document, but only if it hasn't been resubmitted. If you need to know what information has been changed within the document, please speak directly to the individual who resubmitted the document, or ask that the individual adds a comment to the document documenting the changes made.