Zend DB Framework examine query for an update

No, not directly, since Zend Framework builds and executes the SQL inside the adapter method Zend_Db_Adapter_Abstract::update:

/**
 * Updates table rows with specified data based on a WHERE clause.
 *
 * @param  mixed        $table The table to update.
 * @param  array        $bind  Column-value pairs.
 * @param  mixed        $where UPDATE WHERE clause(s).
 * @return int          The number of affected rows.
 */
public function update($table, array $bind, $where = '')
{
    /**
     * Build "col = ?" pairs for the statement,
     * except for Zend_Db_Expr which is treated literally.
     */
    $set = array();
    foreach ($bind as $col => $val) {
        if ($val instanceof Zend_Db_Expr) {
            $val = $val->__toString();
            unset($bind[$col]);
        } else {
            $val = '?';
        }
        $set[] = $this->quoteIdentifier($col, true) . ' = ' . $val;
    }

    $where = $this->_whereExpr($where);

    /**
     * Build the UPDATE statement
     */
    $sql = "UPDATE "
         . $this->quoteIdentifier($table, true)
         . ' SET ' . implode(', ', $set)
         . (($where) ? " WHERE $where" : '');

    /**
     * Execute the statement and return the number of affected rows
     */
    $stmt = $this->query($sql, array_values($bind));
    $result = $stmt->rowCount();
    return $result;
}

You can, temporarily, insert a var_dump and exit inside this method to inspect the sql to ensure that it is correct:

/**
 * Build the UPDATE statement
 */
 $sql = "UPDATE "
         . $this->quoteIdentifier($table, true)
         . ' SET ' . implode(', ', $set)
         . (($where) ? " WHERE $where" : '');
 var_dump($sql); exit;

Use Zend_Db_Profiler to capture and report SQL statements:

$db->getProfiler()->setEnabled(true);
$db->update( ... );
print $db->getProfiler()->getLastQueryProfile()->getQuery();
print_r($db->getProfiler()->getLastQueryProfile()->getQueryParams());
$db->getProfiler()->setEnabled(false);

Remember to turn the profiler off if you don't need it! I talked to one fellow who thought he had a memory leak, but it was the profiler instantiating a few PHP objects for each of the millions of SQL queries he was running.

PS: You should use quoteInto() in that query:

$n = $db->update('pages', $data, $db->quoteInto("url = ?", $content));