Hi, J. This is tough because there are so many kinds of glue. It is also tough because the value of the piece has a lot to do with the answer. If it is a piece of Rookwood or higher quality, I would consider having it professionally repaired. Be aware that any breakage lowers the value of a piece and a poorly done repair lowers it further.
Assuming that it is Woolworth's Best, I would try rubbing the glue with my finger. Sometimes the heat and friction are enough to remove the glue or at least give you an edge to start on. My guess is that it is white glue and soaking the glue with water might soften the glue to where it will start to peel. Put a wet sponge on the spot for a couple of hours. It might help if you had a hobby knife around with a new blade that might let you tease the glue off once you got it softened.