The Plan Item categorization is part of the Agile Planning Component. There is no official API support for the Agile Planning Component. I am not sure how that information is accessed. You would have to debug the Project Area Editor to find how that is working.
									 
									
Comments
Guido Schneider
Apr 20 '18, 4:46 p.m.Hello Reem,
Reem Kadadihi
Apr 23 '18, 2:49 a.m.Hello Guido,
the planning work items (not the Execution Work Items ) in RTC are called top level wrok items.
more under:
https://jazz.net/library/article/589
Br.
Reem.