how do I see my device account number?

If you are referring to the Apple Card, open the Wallet App, click on your Apple Care, click on the three white dots in a black circle in the top right then tap on Card Information.

What do you mean by “device account number?” The phone’s serial number? IMEI? MEID? ICCID? Wi-Fi address? UDID? Something else? None of these are needed in the Wallet app, so most likely it is something else.