Are all Generic Practices (GPs) required for each and every Process Area (PA) when the organization is being appraised? Or there is a main GP for each PA required?
This question is explained in detail in the Intro to CMMI class. If you haven’t already taken the class, I strongly recommend that you take it. Also, if you read the Generic Goal (GG) section of the CMMI book, you read more detail about the GPs.
The short answer to your question is it depends upon the scope of the appraisal and the representation (Staged or Continuous). For Maturity Level 2 all PAs must meet GG2, for ML 3 GG 3, ML 4 GG3, ML 5 GG3. For Capability Level 1 GG 1, CL 2 GG 2, CL 3 GG 3, CL 4 GG 4, CL 5 GG5. But I strongly urge you to take the class and read the model to gain a complete understanding of the answers.