There is currently no function in the API to determine "which component is currently active".
There is "ProMdlActiveGet", but nothing to determine which INSTANCE of that model it is, or where it is in your model tree.
Please create a method, something along the lines of "ProMdlActiveAsmcomppathGet" (or "ProActiveMdlAsmcomppathGet", or whatever) to return the ProMdl of the active model, as well as the ProAsmcomppath down to the model itself.