How to get ParentAssets in Azure Media Services V3?
ParentAssets are available in legacy V2 APIs both .NET & REST apis.
Reference
https://urstream.restv2.westus.media.azure.net/api/Assets('asset id')/ParentAssets".
IAsset.ParentAssets https://docs.microsoft.com/en-us/dotnet/api/microsoft.windowsazure.mediaservices.client.iasset?view=azure-dotnet