Oh, a skill book. Now I really get it! Make it a common event, and give the player options on who to teach the skill to. For example, from Aveyond 2 (one of my favorite games)
North Wind Scroll asks who do you want to teach this spell to? Then it displays two choices, Nicolas or Gavin, and the player chooses who to teach it to. (Yes, I love that game so much that I have memorized that part) :)