When a category skill is learned, the player receives a lore sheet for the category in the turn report. The lore sheet lists the commonly known sub-skills which may be studied anywhere once the category skill is known. Some sub-skills within a category may not be listed in the category lore sheet. These are not directly studyable, even once the parent skill is known. The character is in a city which teaches the skill.
Many cities offer instruction in skills.
The player has a book which teaches the skill.