Does getting a request to review from a professor count me as a reviewer? I got a request to help comment on a paper in a journal from a professor. It's an informal request -- the professor is the one who officially reviews the paper. Can I put "reviewer" in my CV or not?
I think not. Ask yourself what the editor of the journal would think if your CV crossed their desk, and they saw you listing yourself as a reviewer and they'd never heard your name before. Having a review delegated to you does not make you a reviewer for that journal. The journal chose your professor, not you, so you should not muddy the waters about what you've been asked to do. If someone asks you about your reviewing experience, feel free to tell them that you did some subreviewing for your professor.