where do I find the DAN when using the watch?

I used my watch at the Jewel grocery yesterday.

The transaction was over $50 so the clerk asked for a 4 digit number.

I know where to find this on the iPhone for the credit card transaction, but where do I find it for the watch apple pay app?

Is this the DAN device account number or is that a different number?

And in either case, why do I need to find such a number? It is faster to use the card itself instead.

Anyway, I requested the clerk to remove some items and ring 2 separate purchases, each under $50.

Apple Pay on the watch then worked for each.