Many ways to do this. The most general solution, so that you see the result in your 2D window rather than just your layouts, is to use the Floor Plan Cut Plane to look down to the floor below.
The walls that you want to see one the floor above need to have their Floor Plan Display set to "All Relevant Stories" and "Projected with Overhead". With your FPCP set to show down to 1 story below, you should see the walls. To get them to appear dashed, you'll have to apply a Graphic Override (if they weren't dashed to begin with).
Be sure to save all of these settings into a saved View.
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