BI Publisher reports can be found in
The above paths are just for your reference because it might be different in your case. But look for the paths that are highlighted here.
In BI Publisher application, you can obtain the exact location from the "Administration" menu:
Administration > System Maintenance > Server Configuration > In "Catalog" Section, see the value of "Path"
Then you can go to the "Report" folder and search your datamodel with extension .xdm In this File you can see the query