Lost Apple Watch
I haven’t been able to locate my Apple Watch and on find my it says it’s offline, are you able to check it’s last location before it died?
Apple Watch Series 7, watchOS 9
The only way to track a lost or stolen watch is with Find My. See the 'If you don't see your Apple Watch on the map' section in:
If your Apple Watch is lost or stolen - Apple Support
In any case, be sure to put the watch in Lost Mode.