How do I position a donut onto a cube with the corner hanging in between the donut hole? I am trying to get the project on the right to look like the left. I am still in progress but ran into a positioning problem. I can not get the cube in the middle of the donut shape.
Select the cube, enter edit mode and select a vertex on the corner.

Then perss Shift+S to activate the snap function and select "snap cursor to selected" (the 3d cursor will move to the selected vertex).

Exit edit mode

Select the torus object and do "snap selected to cursor".