I think I know what you mean - in WMP click organize/manage libraries and check to see which folders are set as library locations for music, videos etc. If this is what you mean then the answer is...

How can I check this?

I have two Windows 10 PCs (call them PC-A and PC-B) on a hard-wired home network which includes two DLNA devices, a music player and a TV. Both PCs were recently upgraded from Windows 7 Ultimate x64...