How do I find the energy released by uranium fission into Nb and Pr ? Every time I see the equation for some nuclear fission it always just states the energy released but what if we didn't know it as a broader question the elements used before are just an example of a fission equation I saw.
The sum of the actual atomic masses of the reaction products minus the sum of the actual atomic masses of the reacting species gives you the amount of mass converted to energy during the fission. That latter amount can be found by applying $E=mc^2$ to that mass deficit.
As I wrote in my comment, protons cannot be destroyed in nuclear fission, so the atomic number of the fissile nucleus must match the sum of the atomic number of the fission isotopes.
An example of a real calculation can be found here.