If it is a Magician, their realm is Essence. The realm stat for Essence is Empathy, so the applicable stats are Em+Em+Co. A high human would have a racial bonus of +3 for Co and +0 for Em. If they have a Co of 90 (with a +8 stat bonus) and an Empathy of 50 (with a +0) stat, that would total stat bonuses (including the racial bonuses) of +11. Then two ranks of Power Development is +10, so +21. If they take Power Development as a Professional skill (highly recommend), there is a bonus of +1 per rank which in this case is +2, so +23.
They would probably be better off with a higher Empathy to get more of a bonus there, and Power Development is a good choice for your Knack if you are a pure spellcaster so that could be another +5.