She is more than 140 years old and has knowledge of many old diseases and being a witch doctor her pool of knowledge is also help full for many and she had taught chopper under herself all about doctory.
The shipwright in luffy crew Franky is the only p[erson in the world who knows how to make the legendary weapom poseidon during the timeskip he had learned from vegapunks notes and has designed his own armor to fight in series.
Other than just a doctor he is a fighter and had engineered a pill for himself to control his monstyer form which in itself is a great deal which shows his knowledge.
JUdge has been able to create humanoid robot and modify humans dna to create his own army of specialized weapon and he can even clone them and has ceated power rangers in one piece.