Re: Where in the file system is the content I created?
The content (that is, whatever data you input by page editing, adding users, etc.) is in the database that you specify when you install Tiki. It isn't in the file directories. The php files do the logic needed to request and display the site's data. If the index.php file was changed by someone, you can re-upload another copy of the file from the Tiki installation files. There's no particular need to reinstall Tiki in another folder.
What page/file are you trying to see when you get the "unknown column" error? What is the exact wording of the error message?
-- Gary