It is difficult to help because we don't know how the definitions or theorems work.
How do your notes define jump? I have seen it defined exactly as what you are asked to prove.
Have you proved that if is increasing on open interval then (the left-hand limit and the right-hand limit) exist for
If you have that theorem then apply it to this problem.
If not, try to prove it. Or post the theorems and definitions you have to use.