Unfortunately, UG-Post runs in the context of the current work part only. You can get information about the current part, including the part name, but nothing is immediately available regarding any other loaded part.
It is possible, however, to extend the functionality of a UGPost using UGOpen (Ufunc), in which case you could write the information you want to a variable, array, or even to a part attribute, and then read it from UGPost.
Be Well
Tod (1d) Briggs
Manufacturing Solutions Architect
Siemens PLM Software
Detroit, MI