I am new here and have some Question

[simoncn]

The tag is DISCNUMBER (not DISKNUMBER). You can output it but only for the title of the track, not for the title of the album as I thought you wanted. To show it for the title of the track, you can use

Title.displayFormat={$title^$discnumber^ / Disk }

You aso need to add Discnumber to the itemTags property.