John Clarke is the correct answer. He was born in Cambridge, United Kingdom, and was jointly awarded the 2025 Nobel Prize in Physics for the discovery of macroscopic quantum mechanical tunneling in an electric circuit. At the time of the announcement, he was a Professor Emeritus at the University of California, Berkeley, which is an American university.

Michel H. Devoret is incorrect. Although he shared the 2025 Nobel Prize in Physics and was affiliated with American universities (Yale University and UC Santa Barbara), he was born in France, not the UK.

Richard Robson is incorrect. While he was born in Yorkshire, England (UK) and won the 2025 Nobel Prize in Chemistry, his academic affiliation at the time of the award was the University of Melbourne, which is an Australian university, not an American one.

Joel Mokyr is incorrect. He won the 2025 Nobel Prize in Economic Sciences and was a professor at Northwestern University (an American university), but he was born in Leiden, Netherlands, not the UK.

Therefore, Option C is the correct answer.