<%@ Register Src="~/Admin/Controls/ItemControl.ascx" TagName="t" TagPrefix="ctrl" %>
...
<asp:UpdatePanel id="up" runat="server">
<ContentTemplate>
<asp:Repeater ID="r" runat="server">
<ItemTemplate>
       <ctrl:t ID="t" runat="server" Source='<% #Container.DataItem %>' />
</ItemTemplate>
</asp:Repeater>
</ContentTemplate>
</asp:UpdatePanel>

...
<asp:LinkButton ID="lb" runat="server" OnClick="lb_Click" />
...

protected void lb_Click(object sender, EventArgs e)
{
// 
}

protected void Page_Init(object sender, EventArgs e)
{
lb.Click += new EventHandler(lb_Click); // но это не помогает
}