I am an Assistant Professor in the USA and I was invited to be a guest editor of a Special Issue for an international peer-reviewed Journal. I was asked to find 2 other guest editors. Can I invite my PhD student to be a guest editor? Are there any reasons not to do it? I thought it would look good on his CV. I will handle most of the papers, I will give him just 2-3 papers to handle so it won't take too much of his time. He has 2 papers published as first name on this topic.
As someone who served as guest editor already:
I don't see a problem in principle by inviting/recommending an additional person (including students) for this job. I guess I would ask the editorial team, as @Buffy suggested already.
I would not invite a student for other reasons though: Usually this is a lot of work, which blocks students from working on their thesis or related studies. This depends of course if the student wants to do it as an investment in a later career.
Moreover, I think it would be good to have a few years of experience in publishing, which helps you to select reasonable reviewers. This will be different for other fields, but from my experience, there were almost never any perfect fits to reviewers. It was rather hard to identify, who may have expertise in some exotic areas to review a certain paper. Here a few years in the business definitely help. I assume this would be much harder for students - or it would all come back to you rather than taking work away from you.
Keep in mind, even if you give them just 2 or 3 papers, this can result in some serious work, if reviewers don't react or you don't have any good matches from the start, ...
Finally, the statement to "find two other guest editors" somewhat sounds like you would be working with a predatory journal. Without knowing the actual journal, this is how I would interpret this situation.