Run your report in the system where Count Key / Counter column is appearing. Click on one of the fields in that column and press F1. Click on Technical Information Icon and there you will see the structure, field name and data element.
Double click on the field name and see if it leads you to the main structure or an append structure.
2nd option:
SE11 - put the structure name in View. - display
click on append structure - see if there are any append structures created for this particular column to appear.
Thanks.