*sorry I can't give a full explanation.*
g = 9.8 m/s²
w = m*g
Weight of cat: 55 N = m*9.8
m = 5.61 kg
Weight of dog: 110 N = m*9.8
m = 11.22 kg
There is gravitational potential energy (GPE) acting on the cat since it's at the very top.
GPE of cat = m*g*h = 5.61*9.8*2 = 109.96 J
GPE of dog = m*g*h = 11.22*9.8*0 = 0 J (it's 0 m height because it's on the floor instead of in the tree)
But, if the dog was also 2 m up in the tree, its GPE would be 219.91 J.
As you can see, it's GRAVITATIONAL potential energy is bigger than the cat because it weighs more. Generally, if you were just trying to find the force which is w = m*g (since weight is a force), you would see that the bigger the mass, the bigger the force, and gravity stays the same.
Hope this helped