Additional individual counter on Workitems
One answer
One way would be to add an integer attribute then use a value provider script to do the counting.
http://www-01.ibm.com/support/knowledgecenter/SSYMRC_5.0.1/com.ibm.team.workitem.doc/topics/c_customizing_attributes.html?cp=SSYMRC_5.0.1&lang=en
https://jazz.net/library/article/1003