Where to find my Apple Watch IMEI number?

Based on the question as edited by the Moderators,

On the Apple Watch press the Digital Crown and pick the Settings app (grey gear wheel icon)

-or-

In the Watch app of the paired iPhone, pick My Watch

Tap on General, / About and tap again. IMEI is one of the listed parameters

mind you only the cellular apple watches has an IMEI

EDIT: Advice removed, as question has now changed.