KMyMoney is written in C++ so an understanding of C++ will definitely be needed. It would also be a good idea to become familiar with KDE/QT programming.
You will need to have the CVS version of KMyMoney installed as
well as the appropriate development headers. See the requirements section for more
the Install from CVS page which contains
the necessary instructions to get the source directly from the repository.
Don't forget to subscribe to the developer mailing List.