As a result of exporting content MM creates set folders in “Migration Manager for SharePoint\Web Interface\Migration 2007\Export\{JobName}”. Each folder contains export results of a site, list, document library. The folder name comprises the object name and ID (the same names are used for folders with log files). Inside each folder you can find xml files with schema files of the site/list/document library. (Refer the following article for more detailed explanation about xml files: Content Migration XML Schema Reference)Also the folder contains data files with the content to be migrated.
Manifest.xml file of an object with error can be useful for issue investigation. This manifest file is the core migration file, it contains the structure of source site. (For the DeploymentManifest Schema refer the following article).