Which of the following describes a learned person who professes knowledge?

A learned person who professes knowledge is best described by the term "pundit." This word refers specifically to someone who provides their expert opinion or commentary on a particular subject, often in public contexts such as media or academia. The essence of a pundit is their deep knowledge and their role as a commentator, making this choice the most fitting for the description given.

The other terms do not capture the same meaning. "Urbane" refers to someone who is suave, courteous, and polished in manner, lacking the specific connotation of knowledge or expertise. "Prolific" describes someone who produces large quantities of work or output but does not imply any particular expertise or knowledge in a field. "Reprobate" is a term that characterizes someone who is morally unprincipled or an unrepentant person, which does not relate to being knowledgeable or professing knowledge. Thus, the nuanced meaning of "pundit" is what sets it apart as the correct choice.