Hi kankon,

In DataList OnItemDataBound event update the NavigateUrl property to open the url in new tab.

Please refer below sample.

HTML

<form id="form1" runat="server">
    <div>
        <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css" />
        <asp:DataList ID="dlCustomers" runat="server" CellSpacing="0" RepeatLayout="Table" RepeatColumns="2" OnItemDataBound="OnItemDataBound">
            <ItemTemplate>
                <table class="table">
                    <tr>
                        <th colspan="2">Id
                        </th>
                    </tr>
                    <tr>
                        <td>
                            <asp:Label ID="lblId" Text='<%# Eval("Id") %>' runat="server" /></td>
                    </tr>
                    <tr>
                        <td>
                            <asp:HyperLink ID="lnkLink" runat="server" NavigateUrl='<%# Eval("Link") %>'
                                ImageUrl="~/imagefolder/Koala.jpg" ImageWidth="35" ImageHeight="35"></asp:HyperLink>
                        </td>
                    </tr>
                </table>
            </ItemTemplate>
        </asp:DataList>
    </div>
</form>

Namespaces

C#

using System.Data;

VB.Net

Imports System.Data

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[2] { new DataColumn("Id"), new DataColumn("Link") });
        dt.Rows.Add(1, "https://www.aspforums.net/");
        dt.Rows.Add(2, "https://www.aspsnippets.com/");
        dlCustomers.DataSource = dt;
        dlCustomers.DataBind();
    }
}

protected void OnItemDataBound(object sender, DataListItemEventArgs e)
{
    if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
    {
        HyperLink hlLink = e.Item.FindControl("lnkLink") as HyperLink;
        hlLink.NavigateUrl = "javascript:void(window.open('" + hlLink.NavigateUrl + "','_blank', 'width=300,height=200,left=100,top=100,resizable=yes'));";
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As DataTable = New DataTable()
        dt.Columns.AddRange(New DataColumn(1) {New DataColumn("Id"), New DataColumn("Link")})
        dt.Rows.Add(1, "https://www.aspforums.net/")
        dt.Rows.Add(2, "https://www.aspsnippets.com/")
        dlCustomers.DataSource = dt
        dlCustomers.DataBind()
    End If
End Sub

Protected Sub OnItemDataBound(ByVal sender As Object, ByVal e As DataListItemEventArgs)
    If e.Item.ItemType = ListItemType.Item OrElse e.Item.ItemType = ListItemType.AlternatingItem Then
        Dim hlLink As HyperLink = TryCast(e.Item.FindControl("lnkLink"), HyperLink)
        hlLink.NavigateUrl = "javascript:void(window.open('" & hlLink.NavigateUrl & "','_blank', 'width=300,height=200,left=100,top=100,resizable=yes'));"
    End If
End Sub

Screenshot