The reading of the scale depends on the normal reaction force between the scale and your body .
In the first case , the earth exerts a downward force on you .
Hence , to accelerate upwards there needs to be a force acting in the upward direction to counter gravity.
This is the normal reaction force exerted by the scale on you ( and by newton's third law , you exert the same amount of force on the scale).
Hence , we get a non zero reading on the scale ( as reading depends on the normal reaction force)
In the second case , as you are in empty space there's no gravity. But since you are accelerating , there needs to be a force acting on you .
The only force on you is the normal reaction in this case .
So I believe that you would still get a non zero reading on the scale ( as the normal reaction is not zero ).
But the reading of the scale in case 2 is gonna be lesser than case 1 ( infact its half of the reading in case 1) as we have no gravity.
Also , I think we would have no problems standing on the scale . The situation is gonna be similar to standing on the ground and weighing yourself on earth.
Infact , this is the key idea behind einstein's theory of general relativity. Whether we are on earth or on a body accelerating in empty space , the observations are gonna be the same ! .