I recommend at least attending the SCM380 course prior to trying to support the SAP MII product as from the above it's clear you are brand new. The remote BAPI/RFC call for the WM function you are referring to above is located in your MII content in a transaction somewhere in your MII project definition. Perhaps tracking the flow of your process will help you to determine which transaction is making this call.
The NetWeaver Java logs are also a very information place to start as well.
Sam