Please refer this code. All the Textbox are having the same OnTextChangedEvent.
HTML
<table style="width: 99%;">
<tr>
<td width="33%">
Heading1
</td>
<td width="33%">
Heading2
</td>
<td width="33%">
Heading3
</td>
</tr>
<tr>
<td class="Td0">
<asp:TextBox ID="TextBox1" AutoPostBack="true" OnTextChanged="Save" runat="server"></asp:TextBox>
</td>
<td class="Td1">
<asp:TextBox ID="TextBox2" AutoPostBack="true" OnTextChanged="Save" runat="server"></asp:TextBox>
</td>
<td class="Td2">
<asp:TextBox ID="TextBox3" AutoPostBack="true" OnTextChanged="Save" runat="server"></asp:TextBox>
</td>
</tr>
<tr>
<td class="Td3">
<asp:TextBox ID="TextBox4" AutoPostBack="true" OnTextChanged="Save" runat="server"></asp:TextBox>
</td>
<td class="Td4">
<asp:TextBox ID="TextBox5" AutoPostBack="true" OnTextChanged="Save" runat="server"></asp:TextBox>
</td>
<td class="Td5">
<asp:TextBox ID="TextBox6" AutoPostBack="true" OnTextChanged="Save" runat="server"></asp:TextBox>
</td>
</tr>
</table>
C#
protected void Save(object sender, EventArgs e)
{
TextBox textBox = (sender as TextBox);
ClientScript.RegisterClientScriptBlock(this.GetType(), "alert", "alert('" + textBox.Text + "')", true);
// you can write the code here to save the data
}