Beginning August 2016, the FAA no longer requires commercial drone operators to hold a private pilot's license. This requirement has been replaced with an UAS pilot certificate. There is no practical exam to obtain this certification -- only a knowledge test. The test itself is 60-question multiple choice with a 70% score needed to pass. However, it’s not a walk in the park, and a good bit of studying is required. I’d suggest setting aside about 10 to 20 hours. The cost is $150. There are many study tools online, but the best that I have found is on the 3D Robotics website.
A. Find a test center. The 3DR site has a tool to find the closest one. The actual registration process is retro: phone either Computer Assisted Testing Service (800-947-4228) or PSI (800-211-2753). They will take your credit card number and set you up with a times slot.
B. Study! This isn’t like going to the DMV to get your drivers license. You will need to know a lot about airspace, charts, radio frequencies, weather, human factors, etc. This FAA site shows the topics covered. 3DR has a useful study tool, but I wouldn’t consider it comprehensive. You might squeak by the 70% mark with only the 3DR guide, but not with a lot of margin. There’s an FAA study guide, which is boring, but more detailed than the 3DR guide. And if you want more information go to the relevant chapters of the Pilot’s Handbook of Aeronautical Knowledge.
C. Practice exam. After studying a good bit, take the practice exam on the 3DR site. However, I found the actual exam to be A LOT harder than the 3DR practice exam (which was essentially an extension of the FAA practice exam).
D. Take the exam. Be sure to bring a photo ID and lots of patience with you. If you fail the exam you can take it again in two weeks – but you’ll need to pay another $150.
E. IACRA. 48 hours after you pass the exam, go to the Integrated Airman Certification and Rating Application (IACRA) web site, sign up for an account, and enter your Exam ID. After they do a TSA check, you’ll receive your temporary certificate by email. The actual one will arrive a couple of months later.