For this one you need to get all of your mortals to level 52 (49 for Tolten) to get all of their skills and then have your immortals learn all the skills from them using Skill Link. You also need to learn all the skills from the accessories. There are 165 skills in the game to learn. You must also collect all 99 seeds in the game to get an accessory from the pipot. For a list of all 99 seeds, click here.
For a list of all the skills and where you get them, click here.
Also, in this
thread is a list of miscellaneous sidequests and such that will help you getting all the skills.