1. Check whether you're on Desktop or Online first. If you open QuickBooks through a browser and a URL, you're on Online and there's no local file to find; skip the rest of this and just log in. If you open it through a desktop icon, you're on Desktop and the file genuinely lives on a drive somewhere.
2. Find the current location from inside QuickBooks itself. With the company file open, press F2 (or Ctrl+1) to open the Product Information window. The Location field shows the exact folder path the currently open file is sitting in, which is more reliable than guessing based on the default.
3. Check the default path if you never moved anything. On Windows, that's Documents > Intuit > QuickBooks > Company Files, inside a subfolder matching the company name. On a Mac, it's Documents > QuickBooks, usually right alongside the .QBW file's companion files.
4. Look for a network location on a multi-user setup. If multiple people open the same company file, it's likely hosted on a shared drive or a dedicated server running the QuickBooks Database Server Manager, not on any one person's Documents folder. F2 still shows the real path even then.
5. Know what else lives in that same folder. Alongside the .QBW file itself, QuickBooks keeps a .TLG transaction log file (used for crash recovery) and, nearby, a QuickBooksAutoDataRecovery folder holding periodic lightweight copies of your data for the rare case the main file gets damaged.