Hi aspirant,

Gravitation and Center of Mass (COM) both are independent chapters. You do not need to study Centre Of Mass to understand gravitation and vice vers. You can read gravitation. But two thing I would like to say that every chapter in Physics is interconnected and in examination you may find questions which would require  concepts from both chapters. Moreover the weightage of center of mass is more. So you should try to read it also.

Hope I answered your query.