Is there any tool to extract RTC WI Workflow transition to a diagram?

Hi ,

This is a open enhancement :
   Add graphical display of current work item state showing legal transitions (100895)
You may want to add on with more information from your Business Case...

Alternatively, there is a mention of some third party plugins in the work item, that help the visualization, adding it here they are for quick access:
http://blog.stastnarodina.com/honza-en/spot/rational-team-concert-workflow-visualiser
https://jazzpractices.wordpress.com/2013/01/29/what-state-are-you-in-and-where-can-you-go/

hope this helps..

Regards,
Dinesh