Alter Aeon Online Help

Keywords are:  'guild skills'

Certain specialized trade skills are taught within one of the major
guilds. These can be learned from Guildmasters. They do not cost
practices to learn, but they do require the character level,
requisite rank within the guild, and any skill prerequisites.

A Guildmaster can only teach skills of the ranks they can
advance you to.

To obtain a list of what skills are available type 'skills guild'.