Skill Enchanting allows you to strengthen certain skills that have reached their maximum level. You must be level 76 or above and have completed your 3rd class transfer in order to take advantage of this system.
To enchant your skills, simply speak to Agathion Pona. To do this, open your skills window and click on the Skill Enchanting button at the bottom.
Each skill enchant method has a unique success rate, so acquaint yourself with the pros and cons of each. If the skill enchant fails, both adena and SP will be consumed, yet the skill will remain at the same level it was at prior to the attempt. Oh, and don't forget, your success rate increases as your level increases.