If you are using the record selection formula area in the report (not a command), there is a "special field" called "Record Selection Formula" that can be added to the report. In early CR versions, this was often truncated. I'm not sure whether it is in recent versions.
This, of course, is not necessarily the same as the SQL query that gets passed to the database. If not optimized, it will show more criteria than the "show SQL query" area (what actually gets passed), as it will contain criteria that are applied locally.
-LB