addEventListener in a loop – Blancer.com Tutorials and projects

I’m new in this nice community. I am a young student in computer science and I’m trying to develope a web based app to help both sighted people and people with visual empairment to learn typing. My project was blocked by the following problem:
Given a string, I need to verify that the user has pressed the key that corresponds to the first character. If it is correct, the program should test the next character, until the end of the string.
The most natural solutions seems to be a loop, like that:

        do {
        var checkCharacter=lessons[exerciceNumber][2].substr(charNumber, 1);
        document.addEventListener('keydown', testKey);
    }
    while (charNumber<=lessons[exerciceNumber][2].length-1);

When I run the script, nothing appears and it seems it doesn’t detect the pressed keys. Can you help me please?
Inorder to understand the context, I’ll attach the entire file.

<?php
include "config.php";
//Select fields from database
$sql="SELECT lesson_number, exercice_number, text FROM lessons";
$result=$conn->query($sql);
//Pass variables to javascript
$output="<script> var lessons=new Array(); ";
while ($row=$result->fetch_assoc()) {
    $output.="lessons.push([
        ".$row["lesson_number"].",
        ".$row["exercice_number"].",
        '".$row["text"]."']);";
}
$output.="</script>";
echo $output;
?>
<html>
<head>
    <title>Impara a scrivere</title>
</head>
<body>
    <h2 id="lesson"></h2>
    <p id="instructions"></p>
    <p id="check"></p>
    <p id="keyList"></p>
</body>
<script>
    //define variables
    var keys="";
    var exerciceNumber=0;
    var charNumber=0;
    //Function to play the sounds
    function sound(name) {
        var audio=new Audio(name+'.mp3');
        audio.play();}
    document.getElementById("lesson").innerHTML="Lezione "+lessons[exerciceNumber][0];
    document.getElementById("instructions").innerHTML="Esercizio "+lezioni[exerciceNumber][1]+": scrivi <b>"+lessons[exrciceNumber][2]+"</b>.";
    //function to check pressed keys
    funtion testKey(event) {
        if (event.key==checkCharacter) {
            sound ("right");
            keys+=event.key;
            document.getElementById("keyList").innerHTML=keys;
        } else {
            sound("wrong");
        }
    }
    //loop for the exercices
    do {
        var checkCharacter=lessons[exerciceNumber][2].substr(charNumber, 1);
        document.addEventListener('keydown', testKey);
    }
    while (charNumber<=lessons[exerciceNumber][2].length-1);
</script>
</html>