this is not possible from the APIs we provide. The function tree is only one starting to point to start work pages via WorkpageStartInfo-definitions - so when a work page is started, there is no reference back...
Regards, Björn
PS: of couse you may do some "dirty things" like accessing the function tree at runtime and make a walk through the nodes to identify the one that fits to your currently started work page. But this is really dirty..., e.g. an identical WorkpageStartInfo-definition may reside in two hierarchy branches. - So I better not mention it...