Final answer:
The method of scientifically finding the 'one best way to do a job' in scientific management is called Time and motion study.
Step-by-step explanation:
The method of scientifically finding the 'one best way to do a job' in scientific management is called Time and motion study. This method involves dividing different types of operations into sections that can be measured and analyzing them to improve work efficiency. It aims to standardize work and check the efficiency of both people and equipment.