After years of bilateral knee pain, with nothing working, clean xrays and a clean mri, i'm supposed to have bilateral arthroscopy. what can i expect?

Not much !: cannot say in your particular case, but generally, surgery works best on those with the most severe conditions and it hasn't been shown to reliably work unless there is something broken that can be easily removed (bone fragments in the joint). Repairs of broken parts have a poor track record due to other things breaking. If NORMAL on MRI, even less likelihood of dramatic benefit.