bool XPackageEnumerationCallback(  
         void* context,  
         const XPackageDetails* details  
)  

bool CALLBACK ListDlcCallback(
    void* /* context */,
    const XPackageDetails* details)
{
    printf("Found dlc: %s\n", details->displayName);
    return true; // continue enumerating
}

HRESULT ListDlc()
{
    HRESULT hr = XPackageEnumeratePackages(
        XPackageKind::Content,                      /* Looking for content packages (DLC) */
        XPackageEnumerationScope::ThisAndRelated,   /* For this game and related games*/
        nullptr, ListDlcCallback);
    return hr;
}