The weight of anything is (mass) x (gravity in the place where the thing is).
Gravity on Earth is about 9.8 newtons per kilogram, so on Earth,
the weight of the book is
(2.06 kg) x (9.8 N/kg) = 20.19 newtons .
Another way to get around it is:
On Earth, 1 kg of mass weighs about 2.205 pounds, so on earth,
the weight of the book is
(2.06 kg) x (2.205 pounds/kg) = 4.54 pounds .