Try something like this...

private void matchColumns()
               
    {
        string constr = ConfigurationManager.ConnectionStrings["YourString"].ConnectionString;
        SqlConnection con = new SqlConnection(constr);
        con.Open();
        
        string qry1 = "SELECT * FROM tbloriginal";
        SqlCommand cmd1 = new SqlCommand (qry1,con);
        SqlDataAdapter da1 = new SqlDataAdapter(cmd1);
        DataTable dt1 = new DataTable();
        da1.Fill(dt1);
        string qry2 = "SELECT * FROM tblcompare";
        SqlCommand cmd2 = new SqlCommand(qry2, con);
        SqlDataAdapter da2 = new SqlDataAdapter(cmd2);
        DataTable dt2 = new DataTable();
        da2.Fill(dt2);

        for (int I = 0; I <= dt1.Rows.Count - 1; I++)
        {
            string value1 = dt1.Rows[I][2].ToString();
            string value2 = dt2.Rows[I][2].ToString();
            string rowId = dt1.Rows[I][1].ToString();
            
            if(value1 != value2)
            {
               Response.Write ("For NameId " + rowId + ": Column 2 mismatch <br>");
            }
        }

           con.Close();     
    }