Can a school know if you have a degree, if you don't tell them?

[ss20ts]

All of this applies if you are a student with a US degree, seeking to complete another US degree. There is no way a national student clearinghouse based in the US can acquire information about degrees taken in other countries.

Well that depends if you used financial aid. If you used financial aid which is an option for some schools outside of the US, then yes it would be in the clearing house and known to other schools.