if ($("li.nav-item").length == 0) {
            $('span.divider').remove();
        }
        if ($("li.nav-item").length > 0 && $("li.nav-item").is(':visible')) {
            $('<span class="divider"> | </span>').appendTo('li.nav-item');
        }

<ul id="navigation">
                <li class="nav-item"><asp:HyperLink ID="link1" runat ="server" Text="LoremIpsum"      NavigateUrl="#" /></li>
                <li class="nav-item"><asp:LinkButton ID="LoremIpsum" runat ="server" Text="LoremIpsum" PostBackUrl="~/#.aspx"  /></li>
                <li class="nav-item"><asp:HyperLink ID="link2" runat="server"  Text="LoremIpsum" NavigateUrl="#.aspx"/></li>
                <li class="nav-item"><asp:HyperLink ID="linkLogin" runat="server" Text="Login" NavigateUrl="~/login.aspx"/></li>
                <li class="nav-item"><asp:HyperLink ID="linkProfile" runat="server" Text="Profile" NavigateUrl="~/profile.aspx" Visible="false"/></li>
                <li class="nav-item"><asp:HyperLink ID="linkLogout" runat="server" Text="Logout" NavigateUrl="~/logout.aspx" Visible="false"/></li>
                <li><asp:HyperLink ID="LoremIpsum" runat="server" Text="LoremIpsum" NavigateUrl="~/nutzungsbedingungen.aspx"/></li>
                </ul>


if (Session["svar_loggedin"] != null)
    {
        linkLogin.Visible = false;
        linkProfile.Visible = true;
        linkLogout.Visible = true;
    }
    else
    {
        linkLogin.Visible = true;
        linkProfile.Visible = false;
        linkLogout.Visible = false;
    }

$.each($("li.nav-item").children("a").filter(":visible"), function (e) {
    $('<span class="divider"> | </span>').appendTo($(this));
});

linkLogin.Attributes.Add("style", "display:none")

$(function () {
        var elements = $('li.nav-item > a').filter(':visible');
        for (var i = 0; i < elements.length - 1; i++) {
            elements.eq(i).append($('<span class="divider"> | </span>'));
        }

    });