If you need your dad to sign into iCloud on your PC, it's best to be honest about your reasoning. However, if you want to provide a good reason, you could say something like:
"Hey Dad, I need help with something on my iPhone/iPad that's linked to iCloud. If you could sign into iCloud on my PC, I can access some of my photos/files or sync my notes. It would really help me out with [a project, school work, or whatever you're working


