A promissory note can not be discharged. These are legal binding laws that go along with those and they can not be discharged. SOmetimes they can be traded or reduced.
This sort of debt can usually be discharged as part of a bankruptcy, assuming that there is not some other reason why it would not be (student loans, for example).
A promissory note can be discharged within a bankruptcy as long as it is not related to taxes, child support, or college educational loans. It can also be discharged if the debt is forgiven by the lender.