Apple watch series 2

Hi Calnim81,

You started from a great resource: Set up cellular on Apple Watch

The IMEI is available on Apple Watch GPS + Cellular models only. For help with locating the IMEI for an Apple Watch, test the steps below found in the article here: How to find the serial number or IMEI for your Apple Watch

"How to find the Serial Number or IMEI 

1. On your Apple Watch, open the Settings app.
2. Tap General > About, then scroll down.
3. Look for Serial Number or IMEI.

If you don't have your Apple Watch, you can use your iPhone instead:

1. On your iPhone, open the Apple Watch app.
2. Tap the My Watch tab, then tap General > About.
3. Look for Serial Number or IMEI."

You can find more information for setting up an Apple Watch for a family member in the section "Set up cellular on a family member's Apple Watch" in the article you started from. You can also find helpful information here: Apple Watch - Carriers - Apple

Cheers.