* Check online: Many schools have student portals where schedules are accessible. I'd log in and see if my schedule is available there.
* Check with my teachers: I could email or call the teachers of the classes I *think* I have, and ask them to confirm my schedule or tell me what classroom they're in.
* Ask classmates: Friends in my grade might have their schedules and could check if they have any of my classes.
* Go to the main office: The school office usually has master schedules and can print out a copy for me.
* Look for a backup copy: I might have a copy saved somewhere – in a notebook, a folder on my computer, or a photo on my phone.
If all else fails, I would go to the school office as soon as possible to get a replacement schedule.