What are the continued education requirements for commercial / airline pilots?
This question is difficult to answer comprehensively as the continuing education requirements are complex and varied. The complexity is because the continuing education requirements are mandated by multiple parties (the FAA, insurance companies, clients, and employers) and depend on the regulations the flight is conducted under (14 CFR 91, 121, 135, 137, etc.), the type of aircraft operated (single engine, multi-engine, turboprop, jet), and the pilot's role in the operation (PIC, SIC).

Note that both the Commercial and Airline Transport Pilot (ATP) license are good for life, unless revoked or surrendered. Any continuing education requirements are to retain the employment or the privileges of exercising the license, unlike CE requirements for licenses in some industries.

In very broad brush strokes, most professional pilots will be required to complete a flight proficiency check, either in an actual aircraft, or in a simulator, every 6 to 12 months. The amount of time will vary for such checks, but 3 hours might be typical. This proficiency check will be accompanied, in some cases, with a written or oral examination. In addition to this, insurance may require an aircraft systems class and simulator brush up session every 12-24 months. Such training is usually accomplished in 3-6 days, including roughly 12-24 hours of lecture/bookwork, and 6-10 hours of simulator time.

In addition to the flight and systems training, pilots employed by air carriers will generally be required to receive instruction on operational aspects of their operation, including such topics as RVSM, hazardous materials, weather, physiology, as well as many others. Such training is often self-paced, computer based training (CBT). I would estimate the time commitment for this training to be 20-40 hours annually.

In addition to the required training and testing, many pilots choose to spend additional time studying aviation related topics. Such topics may include all those alluded to above, as well as other topics. Examples of such study would be changes to company operational procedures, brushing up on checklist memorization, FAA advisory publications, and areas of interest outside of normal operations, such as international operations. Speaking personally, I probably spend roughly 10 hours a week in what could be considered aviation related study or learning. I also often see other pilots at my company studying various aircraft or operational manuals, and our company keeps a collection of articles, FAA advisories, and other publications related to our operation with the intent that pilots voluntarily study these materials as they have time. Bear in mind that a pilot's life often involves a great deal of waiting, a task which often lends itself to reading and study.