Coolweather–if Turnitin says a paper of my student is similar to another student, they don’t give me information. They say I’d have to write to the student’s institution to get permission–which I’d never bother to do. When one student’s paper sounds like another, it’s generally because they’re cribbing from the same site. So no need to see the other student’s paper.
I honestly find most plagiarism on my own, not through Turnitin. That sometimes give me a lead, but I’m really really good at sniffing it out myself.