Two places. On each delivery date, the Subscription Logs section lists every status change ("Changed to Open/Skipped/Cancelled on <date> by <user>"). For everything else, super admins have a DB Changes button in the page header that opens an audit table with Date, ID, Table, Operation, Change (the exact fields changed) and User, covering the subscription and all its delivery dates, including customer-side actions (pause, unpause, cancel, address requests) and renewal-date changes made when a day is skipped.