What are some advantages and disadvantages of have the wing on top of the airplane?
The SUGAR Volt and SUGAR Freeze concepts use a high wing purely to make effective bracing possible. It is a design for a world where oil costs $200 per barrel and above. Mainly, two things make its aerodynamics much more efficient than current designs:


A very high aspect ratio of its wing, enabled by the bracing, and
A lower flight Mach number, which in turn makes the wing more efficient by requiring less sweep. Boeing doesn't give a Mach number in their web page, but I would bet it is somewhere around 0.75. See here for a discussion of a very similar design.


Todays airliners use a low wing to enable them to stow away their long landing gears and to put the wing spar below the passenger deck. Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Large high-wing aircraft, with their low fuselage position, are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible.

Both concepts use rather speculative engine designs, in case of the SUGAR Volt even one with hybrid natural gas / electric propulsion with onboard batteries. The SUGAR Freeze uses a less speculative engine burning liquefied natural gas. In the SUGAR study, Boeing set the goal to reduce fuel consumption by 70%.