Answer
$5\;\rm kg$
Work Step by Step
Do not be confused about this kind of problem, it is the same reading if you were attaching one of the spring ends to the wall.
It must read 5 kg.
According to Newton's third law, you can mistakenly say that the spring would read zero kg!
That is not right, assume that you are attaching a fish to this scale vertically and you are rising the other end by your hand to read the weight of the fish.
Your hand exerts the same amount of force upward on the scale equal to the weight of the fish and yet the scale reads the weight of the fish, not zero.
