When I remove an old knot the only tools I have available is a hand cranked drill, drill bits, a very small chisle and a small hammer. What I do is first cut off the hair then drill multiple holes using a small drill bit. Then once the old glue is weakend I use the chisle to slowly chip away the remaining glue. I do this very slowly to avoid slipping or cracking the handle.
This is just the way I do it. I'm not saying this is the way it should do.