Sorry Johan for not answering in first place: I tried to use SQL Profiler but I'm not getting anything useful out of it.
For example: this is what system calls when I launch the Inventory Valuation Report (the number on the right is one of my item codes).
exec sp_execute 127,N'005342008'
Maybe it's me but from this I do not understand which procedure is called.
P.s. Is there a way to export the results table in an Excel format? I tried XML table but when opened in Excel it generates an error (error opening file).