Soak a clean cloth in rubbing alcohol.
Dab the ink stain with the rubbing alcohol until you remove the stain or lighten it as much as possible. Work from the edges of the stain as possible and don't rub it as it could spread the mark or work it further into the khaki material.
Rub the stain with liquid laundry detergent until the stain and fabric around it is completely coated. Let it sit overnight.
Rinse the khakis in the morning.
Dab fingernail polish remover onto the stain if it is still visible. Work until the stain is gone.
Launder the khakis as normal.