I was trying to sort some images according to their EXIF creation date or the camery type. To my surprise the columns remain empty although the metadata panel shows the correct values.
If there are a lot of files, you might just need to be patient and wait for the data to load.
Also, the only truly reliable date metadata filed for photos is EXIF DateTimeOriginal. In DOpus, that column is called Date/Time Original.
A photo with no EXIF DateTimeOriginal can still have a 'Date Taken, which nis the English name for the field Aufnahmedatum.