Looking to buy a replacement case how do I find out what issue of tablet I got?

Settings > about

Or if you have the smooth rubberised back with nexus written horizontaly along the length then its 2013 if its a plastic back with the writing across the width then its the 2012.

What if you can’t view it because of the damaged screen?

As above look at the back of the device.

If it has a camera in the back it’s a 2013 if not 2012.

Ah sorry I didn’t read that properly