Hi
If Activation Lock is enabled, then you will not be able to use the Apple Watch.
I suggest that you hand it in to the police, locally to where you found it.
Activation Lock prevents unauthorised use of Apple Watch if it is lost or stolen.
To be able to pair the Apple Watch to your own iPhone, you would need the previous owner to either enter their Apple ID and password on your iPhone or to turn the feature off via https://www.icloud.com/.
You will not otherwise be able to use the watch. There is no way around this security feature.
Apple will not advise you of the previous owner's contact details, nor will Apple pass your details on to them.
More information: