If I understand correctly, what you are trying to achieve can be done via the coordinates palette, specifically the Z coordinate.
If you need to know some element or node elevation (z position), just point to it with tracker or coordinates palette enabled. They will show you the info you're after (z).
You can then type this value in the Z coordinate input box and the working plane will be moved to that value, so if you type 2, the next slab you draw will be 2 (units) above the specified option (project zero, user origin, reference levels) as specified in the palette. This will work in 2D and 2D windows.
Hope this was you were after.
Best regards.