i bought my apple watch second hand and i don't know the original owner to have the lock unlocked what can i do?

Nothing. If you can return it for a refund, do so. If you used a service like ebay, and the seller refuses a refund, file a claim under their buyer protection program.

There is no way to bypass the activation lock.

If you can't get your money back, had it over to the police. It's probably stolen.