Hello Luca, there will be a few approaches to do it.
You could get the average value of the region. If you have a plane via the bulk calculator, there you could select the region option. After drawing a region you will get the average value from that region.
Other options are connected with saving a table of a plane. Go to the edit and change the appearance to shaded gird, refine the gird and save the table. You will later need to delete the points out of scope in excel.
You could simplify the process by adding the volume, which has a common face to the region which you want to check. You could hide all other bodies and take the values from only that face.
BR
Karol