If you want to see what organization Office 365 is activated with, you can take a peek at the user preferences:

defaults read com.microsoft.office

This is a bit tricky, though. At first glance, it might seem

defaults read com.microsoft.office OfficeActivationEmailAddress

is the best indicator of what account is signed in, but that value will remain unchanged if you sign out of that account and sign into a different account. It literally is the email used to activate Office. Once Office is activated, that email will still be the same email that originally activated Office.

A more reliable (if less human-readable) indicator of the organizations is

defaults read com.microsoft.office TenantIDKey

Just keep in mind that Office 365 admins for the org may have a slightly different TenantIDKey from the rest of the org.