Apple Watch series 9 cellular
If I buy Apple Watch series 9 cellular option in US will it work in India
It should, but the warranty is U.S. based, so if you need warranty repair, you have to pay out of pocket, or return to the U.S.
And accepting an Apple Watch intended for a different country is at the discretion of the cellular provider. India does generally accept Apple Watches from other countries, but it is still their decision to make.