I think Bernie is talking about eliminating student debt to the U.S. government, which I am 99% sure can be done through exeutive order.

Almost no chance this is the case. Trump could only wipe out student loan debt for disabled veterans because there was already legislation entitling them to that debt relief, many were just unaware of that and so hadn't filled out the paperwork, or were confused by the process and couldn't complete the application. All the XO did was eliminate the paperwork requirement, essentially.

There is no existing legislation granting student loan debt to the general public, and such a bill would need to be passed in order to do that. An XO alone won't suffice.