I know "the general public" can be use both with a singular verb (when referred to as a group of a whole) and with a plural verb. But what if I want to refer to a single person, who is a member of the general public. Is there a word for it?
From a comment under the question, the following example sentence was provided:
This concept is clear to a scientist, but may be confusing to a ______ (member of the general public).
When referring to a non-scientist (or to anyone who doesn't belong to a specific area of expertise in discussion), the word layperson (or layman) can be used.
: a member of the laity
// Of course, there is also a layperson's theory that usually works.
— Julie Hinds, Detroit Free Press, "Twitter unleashes on Trump for Revolutionary War 'airport' flub," 5 July 2019
// In the spring of 2018 some of these layperson astronomers contacted Vanderburg and told him to check out HD 139139, a sunlike star roughly 350 light-years away.
— Adam Mann, Scientific American, "Astronomers Don't Know What to Make of This Incredibly Bizarre Star," 3 July 2019
From the further definition of laity:
2 : the mass of the people as distinguished from those of a particular profession or those specially skilled
// writers who can interpret this wholeness both to their colleagues and the laity
— P. B. Sears
As such, a layperson is simply a member of the general public inasmuch as they don't belong to a particular group of trained people.
There is another word that's possible, but it's often used in an insulting fashion—even though it's actual definition is more neutral: plebe.
2 a : one of the common people : PLEBIAN
// Once a proud and high-minded group, the new class could look up at the rich with a certain contempt and down at the plebes with compassion …
— Barbara Ehrenreich
2 b : an ordinary person who lacks the knowledge of an insider
// These guys may look like plebes, but they're veteran hackers.
— Davin Coburn
// The movie has its origins in Dave Stevens' 1982 graphic novel (comic book to us plebes), a knowing, exquisitely drawn valentine to aviation aces and 1930s Los Angeles.
— Ty Burr
Unless you are certain of how it will be taken, I would advise against using the word plebe, but I thought it should be included in the answer anyway, since it's still grammatically sound. And if it really is the general public that's being discussed rather than just somebody untrained, then plebe is actually more accurate.