Where can a minor or adult find their social security number online?

You can't. No one can. If you don't know your number and need it, it would be on your federal income tax return and W2 forms. Otherwise you would need to visit the social security office with ID (ssa.gov for a list) and complete an application for a replacement card. When you get that replacement card do NOT carry it around with you; it should be kept at home in a safe place and used only when necessary to avoid identity theft.

Worked for social security for 32 yrs.

You can't. It's protected. Imagine if you could look up anyone's SSN online. IDs would be stolen right and left.

They need to go to the SS office and get a replacement card.

NO ONE should be able to find that info online. It's an invitation to identity theft or other problems.

You can't.

An adult should know it.

It's on your card, your paychecks, and your tax returns.

Hopefully nowhere, or it's easily stolen.

they can't. SSA doesn't allow that