Depends on what kind of stain it is. http://granitecarepro.com/granite-stain-removal.html
I would start with trying out a Magic Eraser!
Food grade hydrogen peroxide will bleach anything. It’s caustic and must be diluted, wear gloves.
It will not bleach oil-based stains. In that case, maybe 70% isopropyl alcohol may help, but not remove it from the pores.