Hi
To check whether an Apple Watch is paired with your iPhone:
On your iPhone, in the Watch app: select the My Watch tab > check for any watches listed at the top of the page.
To check which devices are signed in to your Apple ID account, follow the instructions here:
Check your Apple ID device list to see where you're signed in - Apple Support
If you are concerned that your Apple ID may have been compromised, then follow the instructions here:
If you think your Apple ID has been compromised - Apple Support
If you need further assistance, then contact Apple Support:
Contact Apple for help with Apple ID account security - Apple Support