Of course legal operators are taking the RECURRENT test.
The license doesn't expire but your ability to use the license expires if you aren't CURRENT every 24 months. In order to be current you have to take and PASS the Recurrency Test every 12 months.
I have not seen where to go or how to apply for a renewal. FAADropZone has nothing, and FAA.GOV UAS section does not mention it either. Where / how do we renew?
You take the recurrent knowledge test at an FAA-approved testing center. Once you pass the recurrent test, no new certificate is issued. You will continue to use the original hard copy certificate and keep your most recent test results on your person in case of an FAA check (or a client wants proof that you're current).