Hi @joerghoh to implement my usecase I just need exempted principal list but that should be through api not manuall.
Or if there any property which can that the particular user is exempted that will also work.
No, you cannot detect by an API if a principal is allowed to access a CUG protected resource by this exemption list or by any other means. Because normally it should not matter, and exemption list should only be used for admin usecases.
If you really need to distinguish those 2 cases, you need to implement this feature on your own (as indicated by @arunpatidar ); in any way I would suggest you to create a ticket with Adobe support and raise this requirement there. Pleas include detailled description of your requirement, so product management can evaluate if this is just an edge case or a more common case which might benefit if supported ootb.