Potential energy is stored energy, whereas kinetic energy is energy resulting from an object's motion. Considering the stick of dynamite has not been set off, and there is not motion, it has stored energy. Thus, it is potential energy.
The total mass would be 142.05 g/mol. Since sodium is 22.99 g/mol and there are 2 sodium atoms, it would be 45.98 g/mol. Divide 45.98 by 142.05 and you get 32.37%