I'm getting 2x4 brick pattern mosaic subway tile for my kitchen backsplash. It's in a 12 x 12 sheet. Will I need sanded or nonsanded caulk ?

If the grout joint is 1/8 inch or less you use unsanded. If larger than 1/8 inch use sanded and usually you are matching to the same kind of grout you used for the job. Sanded grout to sanded grout caulk and vice versa.