"Who is the man that makes your cookies?"
Translation:Kim jest mężczyzna robiący wasze ciasteczka?
That would be the formal difference in grammar, but I was asking about the difference in meaning. In Ukrainian for example, the instrumental case inquires about a person's profession whereas the nominative case inquires more generally about a person's name, nationality, etc. So what is the meaning of 'kim' in this sentence and why isn't 'kto' used here?
I think a more or less same distinction works in Polish. "Kto jest mężczyzną [...]? Czy to Paweł, Marek, czy Bartek?" - It sounds as if you really want to know the personal details. "Kim jest mężczyzna [...]" could ask about the profession "Mężczyzna [...] jest nauczycielem/kucharzem/piekarzem", or maybe the nationality (so here it would be a difference) "Mężczyzna [...] jest Polakiem/Amerykaninem/Ukraińcem".
As I said kim is a question of instrumental, and this sentence, has "jest" as verb, mężczyzna....as subject, and question as object in instrumental.
There isn't the kind of difference you explain here.
But there is of course a difference between "Who is the man that makes your cookies?" and "Who makes your cookies?" and I think it is the difference between kto? and kim? you ask about