I assume it's language from the FAA Reauthorization Act of 2018 [1] and specifically § 45509.

Among the requirements for recreational use is "(7) The operator has passed an aeronautical knowledge and safety test described in subsection (g) and administered by the Federal Aviation Administration online for the operation of unmanned aircraft systems and maintains proof of test passage to be made available to the Administrator or law enforcement upon request."

[1] https://www.congress.gov/bill/115th-congress/house-bill/4/te...