You first met Nedicoy while touring Ka'rhashan with Docrath escorting you. After you initially met Mack, you visited a neighboring butcher and ordered a large amount of beef, then made your way to a specialized tattoo artist; the silvered dragonborn Nedicoy.

Docrath left while Nedicoy explained a bit about the city, and explained how his tattoos work.

For 2,000gp of powdered gemstones, he can imbue them with draconic magics and permanence them onto you as a tattoo.

Mechanically these give you stat bonuses, as follows.

Ruby - Strength

Emerald - Dexterity

Diamond - Constitution

Sapphire - Intelligence

Amethyst - Wisdom

Opal - Charisma

You can have only one of each tattoo, allowing you to potentially receive a +1 to each stat for 12,000gp total.