What's the best treatment for pitted skin near hairline? (Photo)

Sorry, you can't undo a bad hair transplant or scars. It's like Herpes. You carry it for life.Only thing you can do is to add more hairs to hide it.  Many have tried resurfacing, derm abrasion, laser, etc.  After spending your time and money, it never is completely satisfactory.  

You could be a candidate for a hairline advancement and total excision of the area using the irregular Tricophytic  hairline advancement technique that we developed 35 years ago. Hair will grow thru and in front of the scar. 

Pitted scar was a complication of older hair transplants with larger skin that were healed and developed a different level (pitted look) at the patients hairline.  Today we are able to remove the follicular units with much smaller punches that leaves no scarring on the recipient what so ever. The old pitted scars could be removed by FUE punches of larger sizes and leave the wounds to heal primarily.  In most cases that is the only treatment you need.  The hair that is removed from those area could be trimmed under microscope and reused in other areas as well.

Without examining you, I can not tell what I would do. I have been repairing old plugs and the complications of them for 24 years, so I have developed an entire approach to it, something I can not write here as it would be like a text book

This is common to get after removing the huge old plugs.  We usually recommend taking the old plugs out and do a refined hair transplant to cover it.