Items in list list are not showing

You'll find it odd System.Linq.Enumerable+WhereSelectListIteratorbecause it 's the representation ToString()of the list iterator , which is returned by the f.Clients.Select(y => y.NomClient)query .

If you need to display all NomClientvalues, it is recommended that you build a concatenated string of them:

public static void generateCTAF(string pathXml, string outputPDF)
{
    List<FichierCTAF> fc = getXmlFCtaf(pathXml);

    foreach (FichierCTAF f in fc)
    {
        Console.WriteLine("ID CTAF : {0}\n Nom Client : {1}\n\n", 
           f.IdFichierCtaf, 
           String.Join(", ", f.Clients.Select(y => y.NomClient)));
    }
}

Alternatively, you can enumerate NomClientsthe values ​​and print each value on its own line:

public static void generateCTAF(string pathXml, string outputPDF)
{
    List<FichierCTAF> fc = getXmlFCtaf(pathXml);

    foreach (FichierCTAF f in fc)
    {
        Console.WriteLine("ID CTAF : {0}", f.IdFichierCtaf);

        foreach(string nomClient in f.Clients.Select(y => y.NomClient))
            Console.WriteLine(" Nom Client : {0}", nomClient);
    }
}