Hi akshayes004,

Refer below code.

HTML

<asp:Button ID="btnAdd" runat="server" Text="Add" OnClick="AddTextBox" />
<asp:Panel ID="pnlTextBoxes" runat="server"></asp:Panel>
<asp:Button ID="btnSave" runat="server" Text="Save" OnClick="SaveAll" />

Code

protected void Page_PreInit(object sender, EventArgs e)
{
    List<string> keys = Request.Form.AllKeys.Where(key => key.Contains("txtDynamic")).ToList();
    for (int i = 1; i <= keys.Count; i++)
    {
        this.CreateTextBox("txtDynamic" + i);
        i++;
    }
}

protected void AddTextBox(object sender, EventArgs e)
{
    int index = pnlTextBoxes.Controls.OfType<TextBox>().ToList().Count + 1;
    this.CreateTextBox("txtDynamic" + index);
}

protected void SaveAll(object sender, EventArgs e)
{
    for (int i = 0; i < pnlTextBoxes.Controls.OfType<TextBox>().ToList().Count; i++)
    {
        string textuom = pnlTextBoxes.Controls.OfType<TextBox>().ToList()[i].Text.Trim();
        string textitem = pnlTextBoxes.Controls.OfType<TextBox>().ToList()[i + 1].Text.Trim();
        i++;
        var X = 1;
        // You code for saving the TextBox value.
        string constr = ConfigurationManager.ConnectionStrings["myconnection"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("INSERT INTO GATETABLE (NAME,ID,ITEMs,DEPARTMENT,IS_ACTIVE,CREATION_DATE,RECORD_ID,ITEM_UOM) VALUES (@NAME, @ID,@ITEMs,@DEPARTMENT,@IS_ACTIVE,@CREATION_DATE,@RECORD_ID,@ITEM_UOM)"))
            {
                cmd.Connection = con;
                cmd.Parameters.AddWithValue("@Name", txt_name.Text.ToString());
                cmd.Parameters.AddWithValue("@ID", txt_ID.Text.ToString());
                cmd.Parameters.AddWithValue("@ITEMs", textitem);
                cmd.Parameters.AddWithValue("@DEPARTMENT", txtdept.Text.ToString());
                cmd.Parameters.AddWithValue("@CREATION_DATE", dateToday);
                cmd.Parameters.AddWithValue("@IS_ACTIVE", X);
                cmd.Parameters.AddWithValue("@RECORD_ID", recordId);
                cmd.Parameters.AddWithValue("@ITEM_UOM", textuom);
                con.Open();

                cmd.ExecuteNonQuery();
                con.Close();
                ScriptManager.RegisterStartupScript(this, this.GetType(), "red‌​irect", "alert('DETAILS SAVED SUCCESSFULLY'); window.location='" + Request.ApplicationPath + "textbox.aspx';", true);
            }
        }
    }
}

private void CreateTextBox(string id)
{
    Literal ltuom = new Literal();
    ltuom.Text = "UOM : ";
    pnlTextBoxes.Controls.Add(ltuom);
    TextBox txtuom = new TextBox();
    txtuom.ID = id;
    pnlTextBoxes.Controls.Add(txtuom);

    id = "txtDynamic" + (Convert.ToInt32(id.Replace("txtDynamic", "")) + 1);
    Literal ltitem = new Literal();
    ltitem.Text = "ITEM : ";
    pnlTextBoxes.Controls.Add(ltitem);
    TextBox txtitem = new TextBox();
    txtitem.ID = id;
    pnlTextBoxes.Controls.Add(txtitem);

    Literal lt = new Literal();
    lt.Text = "<br />";
    pnlTextBoxes.Controls.Add(lt);
}

Screenshot