Can’t get my sons lost iPhone verification code

You can sign in to locate it without needing a two-factor code. Use any internet browser and log into www.icloud.com/find

Note that you need to use that exact address (with the "/find") in order to do it without a two-factor code.

Also see the following Apple articles for information about lost or stolen iPhones or iPads: If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support and

Use the Find My app to locate a missing device or item - Apple Support