If your Data Transfer Files are not appearing on your MacBook Air running macOS X, you might want to try these steps:
1. **Restart the MacBook Air:** Sometimes, a simple restart can solve various issues, including missing files.
2. **Check the Source Device:** Ensure that the device you're transferring the files from is properly connected and accessible. If it's an external storage device, make sure it's plugged in and recognized by the MacBook Air.
3. **Check Finder Preferences:** Open Finder and go to Preferences (Finder > Preferences). Under the "General" tab, make sure that "External disks" and "CDs, DVDs, and iPods" options are selected to show these devices on the desktop and in Finder.
4. **Check Sidebar Settings:** In Finder, click on "Finder" in the menu bar and then select "Preferences." Go to the "Sidebar" tab and make sure that "External disks" and "Removable media" are checked.
5. **Use Disk Utility:** Go to Applications > Utilities > Disk Utility. Check if the device or drive you're transferring files from is recognized here. You can try repairing the disk if needed.
6. **Check for Updates:** Make sure your macOS is up-to-date. Sometimes, issues can be resolved with system updates.
7. **Check Drive Format:** Ensure that the external device's format is compatible with macOS. If it's using a Windows-specific format, you might need to reformat it to a format like exFAT or FAT32 that's readable on both macOS and Windows.
8. **Check Other Users:** If you have multiple user accounts on your MacBook Air, make sure the files aren't appearing in a different user account's directory.
9. **Use Terminal:** If you're comfortable with the command line, you can use Terminal to navigate to the directory where the files should be and check if they're there.
10. **Check iCloud and Cloud Services:** If the files are stored in iCloud or other cloud services, make sure you're signed in and the files have properly synced.
11. **Check Hidden Files:** Sometimes, files might be marked as hidden. In Finder, press Command + Shift + Period to toggle hidden files visibility.
If none of these steps work, you might want to seek assistance from Apple Support or visit an Apple Store for further troubleshooting.