<?php

include "../banco_de_dados/banco_cadastro.php";

$sql= mysql_query("SELECT * FROM rank ORDER BY pontuacao DESC");

echo "<table>";
echo"<th > Colocação  </th> <th> Nome </th>  <th > Pontuação </th> ";

$num=1;

while ($row = mysql_fetch_array($sql))
{
echo "<tr>";
echo"<td >" . $num . "º</td>";
echo "<td  > " .$row['nome'] . "</td>";
echo "<td > " .$row['pontuacao']. "</td>";
echo"</tr>";

$num++;
}

echo "</table>"; ?> </div>

SELECT COUNT(*)+1 FROM rank WHERE pontuacao>(SELECT pontuacao FROM rank WHERE email = '$email' )

$email = (EMAIL DO USUARIO LOGADO); // Sanitize para evitar SQL Injection.
$query = "SELECT COUNT(*) + 1 AS colocacao FROM rank
          WHERE pontuacao > ( SELECT pontuacao FROM rank WHERE email = '$email' ) ";
sql = mysql_query($query);
...

SELECT COUNT(DISTINCT Pontuacao) FROM rank;

SELECT Count(DISTINCT Pontuacao) FROM rank
WHERE Pontuacao < (SELECT Pontuacao FROM rank WHERE email = EmailDoUtilizador);

colunas 100
        101
        500

cadastro[0] = 100
cadastro[1] = 101
cadastro[2] = 500