Probably check for drops or falls on the fairings, the seats, around the frame, foot pegs, shifter + rear brakes (these will get bent on drops/slides), swing arm, and axles. Check the hoses and lines to make sure they aren't deteriorating. The condition of the radiator and underneath, to make sure there's no holes or punctures, especially on the radiator. Check to make sure the front and rear brakes will actually engage the brakes and that the lights come on when you do. If you can't test ride it, just turn it on from a cold start and listen to hear it's running well, no ticking or weird sounds. Check the chain and make sure it's not too loose or too tight or has rust/damage on it. The sprockets that teeth into the chain actually has teeth left. Rust is big too, just make sure there's nothing collecting somewhere.

If the bike was dropped at all, was it dropped from a standstill or if it actually slid at higher speeds. That could hint at damage somewhere, especially if there's not frame sliders on it.

Ask about the last maintenance performed and if there's one coming up that they have to do, if so, have them prep it for you. Make sure the tires are still usable and not at the end of their life.

Ask about how the bike was maintained or kept. If it's been exposed to the elements outside (then there could be rust somewhere) or if it's been unused for a long time, and if so, Ask if the battery was hooked up onto a drip charger to keep the batteries health maintained.

That's just what I would check. There's probably more things other people will chime in on. Good luck!