/Users/<username>/Library/Application Support/Zotero/Profiles/<randomstring>

Note: The /Users/<username>/Library folder is hidden by default. To access it, click on your desktop, hold down the Option key, and click the Finder's Go menu, and then select Library from the menu.

C:\Users\<User Name>\AppData\Roaming\Zotero\Zotero\Profiles\<randomstring>

Note: If AppData is hidden on your system, click the search bar (or Start before Windows 10), type %appdata%, and press Enter, which should take you to the AppData\Roaming directory. You can then open the rest of the path.

C:\Documents and Settings\<username>\Application Data\Zotero\Zotero\Profiles\<randomstring>

~/.zotero/zotero/<randomstring>