As far as I know, this is not natively supported by Windows IoT.
The closest term I can think of is KnownFolders, but network shared folders don’t seem to be included.
However, the workaround you can try is using FilePicker, when browsing the filer, type the network shared folder address in the address far, see if you will get any AccessViolation exception when reading/writing files.
Update, FilePicker does not seem to work either!
Also, I’ve tried node.js to access network shared smb files, still does not work with Windows IoT.
So far, the answer seems impossible to me.