Unfortunately, PP doesn't show you this info.
Not directly PJ, but if you have not Saved the Project, after accepting the Media Offline, usually by choosing Offline Media, or Skip All, when PrPro asks "Where is file _____ ?" You might have an earlier AutoSave, that has not been told to Offline the Media. Now, if you DO have such a Project (PRPROJ file), when PrPro asks "Where is file _____ ?" not the folder, in which the Finder opened, as that is where PrPro expected to find the file.
This ARTICLE goes into a bit more detail on Media Offline.
Another method, would be to Open your older PRPROJ file in, say Word, and do a Search for one of those Offline files, looking carefully at the Path.