It looks like you are in Iowa. The Iowa state government has a form to obtain license:
They have also posted a lot of related information about building code, license fees and a lot more. http://idph.iowa.gov/PMSB
You may also want to explore organizations like Iowa Skilled Trades (https://iowaskilledtrades.com) and the The Mason Contractors Association of America (https://www.masoncontractors.org/masonrycareers/careerinformation/)
Brian recommends the following next steps:
If you live in the US many trades are most likely licensed by your state Department of Licensing. A call there, or maybe checking if they have a website, ought to get you the info you are looking for. In your state, the department may be called something different, but you'll find it. We need more stone masons! Good luck.