If you want to check that the existing CUE files are completely imported you can just open the "Audio -- Task -- Incomplete albums" smartlist. This will display albums that have missing tracks (should only happen if you removed/deleted them from MC)
To check if whole CUE files are not imported, Labinksi's suggestion is the easiest way - just run an Import on the Audio folder and then open the "Recently Imported" playlist. This will show both the entire CUE albums that were just added, and also individual tracks that were missing and are now reimported from their original CUE. If you don't want these newly imported files/albums on MC you can just delete them again from this smartlist (or do a Library Backup before you do this import, then do a Backup Restore)
MC tracks files/albums that were previously imported, even if you delete them afterwards. So it's possible that nothing will get Imported because they had been previously imported already. To avoid this you need to do one of the following:
- clear the Removed database (search for "~d=r" on MC and delete everything from there - search these forums for more instructions if needed)
- or, uncheck the "ignore files previously removed from library" on the Import dialog