Click on Windows8_OS(C:). This will expand your root directory. Click on users in the expanded root directory, Click on your own directory and then you will see a onedrive directory. This is the directory that is listed separately near the top of  windows explorer. In gretl you can navigate to it and set it as default working directory (|File|Working Directory| in gretl). If you save any data, gretl scripts, graphs etc. in this directory they will be available in one drive as if you worked from the link to one drive.