An easy way is to go to https://nipr.com/help/look-up-your-npn.
Background: The insurance regulators saw a need to identify problem producers. In the past, individuals could move from a state where they had problems to a new state and apply for a resident license there. When they got in trouble there, they moved on. National Producer Number (NPN) fixed that issue. Some states use the NPN as the producer’s license number.