Hi  smile,
Please refer below sample.
HTML
<div>
    Total :
    <asp:TextBox ID="txtTotal" runat="server" />
    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:BoundField DataField="AdmissionNo" HeaderText="Reg No." />
            <asp:BoundField DataField="ReferenceNo" HeaderText="Ref No." />
            <asp:BoundField DataField="SName" HeaderText="Student Name" />
            <asp:BoundField DataField="FName" HeaderText="Father Name" />
            <asp:BoundField DataField="FPhone" HeaderText="Phone No." />
            <asp:BoundField DataField="SubjectName" HeaderText="Subject" />
            <asp:TemplateField>
                <HeaderTemplate>
                    Obtain</HeaderTemplate>
                <ItemTemplate>
                    <asp:TextBox ID="txtObtain" runat="server" Text="0"></asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
</div>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script type="text/javascript">
    $(function () {
        $('[id*=txtObtain]').on("blur", function () {
            var totalMarks = $("#txtTotal").val();
            if (parseInt($(this).val()) > parseInt(totalMarks)) {
                alert('Obtain Marks should be less than Total Marks');
                $(this).val('');
                $(this).focus();
            }
        });
    });
</script>
Namespace
C#
using System.Data;
Code
C#
protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[] { new DataColumn("AdmissionNo", typeof(string)), 
                                            new DataColumn("ReferenceNo", typeof(string)), 
                                            new DataColumn("SName", typeof(string)), 
                                            new DataColumn("FName", typeof(string)), 
                                            new DataColumn("FPhone", typeof(string)), 
                                            new DataColumn("SubjectName", typeof(string)) });
        dt.Rows.Add("A1", "R1", "SN1", "FN1", "123344556", "English");
        dt.Rows.Add("A2", "R2", "SN2", "FN2", "222222154", "Maths");
        dt.Rows.Add("A3", "R3", "SN3", "FN3", "565656656", "Hindi");
        this.GridView1.DataSource = dt;
        this.GridView1.DataBind();
    }
}
Screenshot
