The phrase ‘What’s Your 20?’ comes from a system of radio codes called the 10 codes . They were developed in the 1930s when police started using 2-way radio and were designed for brevity and clarity.
It’s a similar idea to Q-codes developed around 1909 that were used in British shipping and later adopted my radio hams around the globe. Although developed when radio was exclusively morse code, they continued to be used when voice transmissions were introduced.
In an environment where interference could play a big role in the understanding of a transmission, ten codes increased the chances of the radio call being understood.
Interestingly, the “ten” was actually added to the beginning because in the early days of radio that used valves there was a slight lag time before full power was achieved. Radio operators were told to pause briefly before talking but often forgot. Having the extra syllable gave this extra, often vital, time.
When the CB radio craze hit, the ten codes were borrowed from law enforcement and adapted for CB use by truckers who popularized these codes along with the CB slang that we’ve all come to love and associate with the hobby.
One ten code in particular was 10-20 which referred to location. What’s your twenty literally means – Where are you? / What’s your location?
So, there you have it. If someone on CB wants to know your twenty then they are referring to the ten code, 10-20 and want to know your location.