<itemtemplate>
    <div class="Class1 subclass1 subclass2 ">
        <asp:RadioButton CssClass="Class2" ID="rbOne" runat="server"
            GroupName="GroupItems"  />
        //Some other controls

        <asp:Panel class="myPanel mYText" style="display:none;" runat="server" id="MyPnl">
            <asp:TextBox runat="server" ID="tbValue" CssClass="SomeClass" MaxLength="11"
                    Text=""></asp:TextBox>
        </asp:Panel>
    </div>
</itemtemplate>

$('div.Class1 input[type=radio]').on('change',function(){
    $(this).nextUntil('.myPanel').find('input.SomeClass').val()
})

document.getElementById('<%=tbValue.ClientID%>').value;

<asp:RadioButton CssClass="Class2" ID="rbOne" runat="server" onchange="RadioClicked(this);"
                                        GroupName="GroupItems" onclick="GetValue()" />

function RadioClicked(rad)
{
     alert("change fired");
     alert($(rad).closest('.Class1.subclass1.subclass2').find('.SomeClass').val());
}

function RadioClicked(rad)
{
      alert($('<%= tbValue.ClientID %>').val());
}