Scott McCloud is an very successful and well-known cartoonist. One of his comic books is Understanding Comics, a non-fiction text that “explains the inner workings of the medium and examines many aspects of visual communication.” http://scottmccloud.com/2-print/1-uc/
Given his background, it is easy to argue that McCloud’s Understanding Comics is “reliable knowledge.”
Whether or not McCloud’s comic book “lack[s] certainty” is another matter. Given McCloud’s expertise it could be argue that it does not lack certainty. The fact that it is a comic book about comic books could be another way to argue that it has certainty. However, it isn’t an academic text and from some perspectives McCloud’s comic book does not high enough standards to have enough certainty. McCloud’s comic book could be compared / contrasted to an academic text on the same topic.
With November 2020 TOK Essay Prescribed Title #6 and this RLE, the focus needs to be on whether or not McCloud’s reliable knowledge can lack certainty.