Try assigning a material that has a density property defined and see if the Mass and Volume are calculated.

In Mechanical, click on the body named SURF under the Geometry branch. In the Details window is a Material branch and an Assignment line. Use the pulldown to select Structural Steel, which is the default material and has a density.

If that worked, you can open Engineering Data and create your own material with a different density, and change the assignment in Mechanical.