Ranks and Skilll Points
Spending skill points to gain extra areas of specialized skills such as Knowledge or Perform is unrelated to spending skill points on ranks.
For example, a 1st level character with Academia could spend 4 skill points on the skill group, gaining 4 ranks in one type of knowledge. He could then spend additional skill points to buy other areas of knowledge (as many as he wanted, at a cost of 1 point per area).
Note that a new area costs 1 skill point, not ‘one rank in the skill’, so you can’t get new areas as part of a skill group, you have to buy them separately. (the first area comes free as part of getting 1 rank, so you don’t need to spend a skill point on it).
When you gain a rank in one of these skills, it applies to all specializations you possess in that skill (including if you got the rank via a skill group). When you purchase a new specialization, it starts with the same number of ranks as your existing specializations.
Skill Specializations and Skill Focus
See Skill Focus for details.