text/koot_nightwatch_ch1/1 matches the site

public static LinguisticObject Koot_Chapter()
{
    var chapter = new LinguisticObject()
        .WithContext()
        .WithId("https://linked.art/example/text/koot_nightwatch_ch1/1")
        .WithLabel("Chapter 1 of Koot")
        .WithClassifiedAs(Aat.Chapter, Aat.TypeOfWork);

    chapter.IdentifiedBy = [new Name("Introduction").AsPrimaryName()];

    chapter.PartOf = [
        new LinguisticObject()
            .WithId("https://linked.art/example/text/koot_nightwatch")
            .WithLabel("Koot's Night Watch")
    ];

    return chapter;
}

• Metatype classification The second argument classifies the first, not the object: WithClassifiedAs(Aat.Description, Aat.Statement) says this is a Description, and Description is a kind of Statement. The Plain C# form shows the nesting.
• Role shortcuts AsPrimaryName, AsAccessionNumber and AsSystemAssignedNumber each add a single classification, with the AAT terms Primary Name, Accession Number and System Number.

var linguisticObject = new LinguisticObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/text/koot_nightwatch_ch1/1",
    Label = "Chapter 1 of Koot",
    ClassifiedAs =
    [
        new Type("http://vocab.getty.edu/aat/300311699", "Chapter")
        {
            ClassifiedAs = [Aat.TypeOfWork],
        },
    ],
    IdentifiedBy =
    [
        new Name("Introduction")
        {
            ClassifiedAs = [Aat.PrimaryName],
        },
    ],
    PartOf =
    [
        new LinguisticObject
        {
            Id = "https://linked.art/example/text/koot_nightwatch",
            Label = "Koot's Night Watch",
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.