I have a scratch about the width of a knife blade.  The scratch doesn't seem to be that deep, even though it shows up as white on a black car.  Does this mean it is all the way to the metal ?  I can't really catch my finger nail in it.  It is probably about 10"-12" long.

Would a paint pen be a good choice for something like this ?  Or does a scratch this long require spraying ?

I would appreciate your thoughts.  Thanks !

Yes, a paint pen would work well. The nib of the paint pen has a chiseled end so you can put it on the side and do very thin scratches with it.