A couple of options.
If you know about this requirement in advance, model a body that represents the volume, use component control to disable it and then use it for volume goals or volume parameters. It would be similar to the method described here: https://forum.solidworks.com/thread/64443?tstart=0
If it is just a small area (surface region) that you're interested in, the same holds true except that the component you're going to use to measure with would be smaller and that you'd use a surface goal/surface parameter for the measurement.
If you don't know, I think your best bet would be point parameters using XYZ locations. If you have enough of them, you should be able to get a good idea of what is happening in a volume or area that is defined based on those points.
I think more commonly most customers create multiple cutplots and use the probe tool to know what is happening in a volume. However it is more subjective because you're looking at contours rather than raw data.
I often use XY plots to track data like this. I often create multiple horizontal lines and use the vertical axis (model Y-axis) as the ordinate. In this way you can get columns of X,Y data points into Excel directly.
I've never tried, but you might be able to use 3D sketches to define these also to make it easier to gather a field of data points.
Thanks to both of you for the suggestion. I think I will give a go for method suggested by Chris for the 3d sketches.
Thanks a lot.