Answer:
N=0
Explanation:
If we take the two cubes as one whole object, we can see that there is no floor to support them, therefore there is no force acting against the cubes when free falling.
If we look at each individual cube, they will hardly be in contact, the bottom cube has no additional support (does not lie on any surface) to go against the weight of the top cube, therefore it doesn't apply any force to the cube on top.
They will be both falling with the same acceleration at the same rate. So there will be no force acting between the two of them.
This is the exact same situation you have on a falling elevator, you will have an ilusion of there not being gravity, but this is because the elevator and you are falling at the same rate, so there is no normal force between the floor of the elevator and you.
