where is the Documents folder shown in iFile (iPad-Air)? There is a folder called Documents (and other folders beside that) in iFile

I tried but can't find the physical location with iFunbox or iTools.

How can I find the physical location of that folder?
When using a system that doesn't know how to follow POSIX symbolic links (like iFunbox), then you're going to need to know the actual location of the directory. When using iFile, it'll appear to be located at /var/mobile/Documents/, but in reality, /var is a symbolic link to /private/var/. So the answer to your question is: The Documents folder is located at /private/var/mobile/Documents/.