Hi Rakshan,
You do not need certification to get into a PMO job. PMO is all about Project Management Skills in turn stemming from experience and expertise in the area. If you are considering HR PMO then it is highly strategic in nature. It is prevalent in any area wherein projects / programs are being implemented. Most organizations run PMO's for various HR arms such as L&D, Operations, Shared Services, HR-IT etc. You must imbibe a thorough sense of the vertical from a practical sense and then work on projects in that dept. You may be working with other coordinators sitting out of the host country / location to standardize the program universally (at all locations).
For more information what's your current role and JD?