Is iwatch 7 unlocked or not?

If you want the GPS+Cellular version of the watch, it is not "locked" but the watch and iPhone MUST use the same carrier and there is generally an additional monthly fee to support the watch by that carrier. See:

Set up cellular on Apple Watch - Apple Support

"Make sure that you have an eligible cellular service plan with a supported carrier. Your iPhone and Apple Watch must use the same carrier, and you must be within your carrier's network when you set up cellular on your watch." Be aware that if it works with the carrier in India, then it may not work anywhere else outside that country. The watch will not "roam" outside the network it is setup in.

If you get the GPS-only version of the watch, then none of the above matters. It will work with your iPhone wherever you are. A GPS-only watch can do everything the GPS+Cellular version can as long as it is near the paired iPhone. (And there is no additional monthly fee.)

No Apple Watch is locked to a carrier unless I suppose you buy it from a carrier under a subsidized plan. But if you are planning to buy a US Apple Watch and send to your dad in India, DON'T DO IT. Apple Watch is sold regionally. An US bought Apple Watch which is cellular, will work in the US, Canada, Mexico and Puerto Rico. It's not supposed to work with cellular providers in India. It also will have no warranty in India and it ever needs warranty service, it will have to physically be brought back to the US.

A better solution would be to buy your dad a gift card from Apple in India, and let him buy his watch where he will use the watch.