Apple watch

The person that you got this watch from needs to follow all the steps in this link;

Remove the Activation Lock so that the buyer can use it.

If they can't or won't then recycle the watch and put it down to a bad experience.

If the Apple Watch is activation locked: How to remove Activation Lock – Apple Support (UK)

Basically, if he can’t remember his Apple ID login (which he should find out and write down for future), you need the original proof of purchase, and you should visit an Apple Store or contact them.