Depends how deep it is.
If your car has a clearcoat, ie metal,primer layer,paint then clearcoat & the scratch has gone through to the paint there is not an easy solution apart from respray on that area, bonnet one of the better panels to do, rear quarters etc are a right nightmare as the clearcoat needs to be blended in some where else you get a nice ridge!
If your car has just paint (only older cars have this type) provided there is enough paint depth you would be able to polish it out.