How do I remove this marker mark on painted drywall?
Once it's been painted over, there's no way to remove a stain - you'd have to remove the paint to get at the stain, which is definitely not "minimal effort".

The simplest thing to do at this point would be to call back the contractor and have him actually paint the wall, rather than just slapping on some paint-like substance and calling it good. There is simply no way those marks would still be showing through if the contractor had done a proper job, with a stain-blocking primer and a good-quality paint.