Question

Identify one belief about the afterlife that the major monotheistic religions have in common

Answer 1

Let's list the major monotheistic religions: 

Christianity
Judaism
Islam

They are all Abrahamic religions, that is they go back to the story of Abraham. 

All of those religions describe the afterlife as something good, much better than the life on earth, but also as something that has to be deserved : Afterlife needs to be deserved and this is what motivates people to be good people on Earth. 

(Afterlife is/can be better than life on Earth: that's one belief)

Answer 2

One belief about the afterlife that the major monotheistic religions have in common  is the afterlife as something good.