My solution with added improvements-how to show users the paired up answers to their list of wrongly answered questions?

//questions stored as an array
let questionAnswerPairs = [
  ['What is 7 multiplied by 9? (write your answer as a number)', '63'],
  ['What is the capital of Belgium?', 'Brussels'],
  ['Which actor plays the comic book character "Captain America" in the MCU?', 'Chris Evans'],
  ['Who is the current US president (first and last name)?', 'Donald Trump'],
  ['Which football team won the 2019 UEFA Champions League final?', 'Liverpool']
];
//Variables declared and initialised below:
let correctAnswers = 0;
let questionResponse;
let correctlyAnsweredQuestion = [];
let incorrectlyAnsweredQuestion = [];
let resultsSummary;

/*Updated the print function to include a modern way of posting output to the HTML document/manipulating the DOM of the web page, rather than using document.write().
Targets specific ID tag to print html content inside of that element, rather than just printing to the web page generally.
getElementByID is a method of the document object that located a tag with a specific tag attached to it.

outputDiv is a variable which holds an object with a reference for a particular spot on a webpage matching the provided string.
Called the node.
*/
function print(message) {
  let outputDiv = document.getElementById('output');
  outputDiv.innerHTML = message;
}

/* Main logic loop for the program below.
This loop uses a for-loop to cycle through each question in the array, and check the stored response-provided via a prompt method- against the answer stored in each array within the questionAnswerPairs array above.

Using prompt over creating a specific variable for the question for succintness 

Validation- checks if a response is entered using a while-loop. Repeatedly asks the question indicated by the current index value of the variable i until the user provides a response.

Normalisation- to keep presentation neat, the string answers stored in questionAnswerPairs are capitalised where appropriate. Using toLowerCase() method on strings, we normalise this answer and the user input (questionReponse) to anticipate unanticipated behaviour by users.

If correct, then the int value of correctAnswers is increased by 1 accordingly.
Then we store that particular (according to the current index value of the for-loop) element from questionAnswerPairs array (itself an array comprised of a question & answer) in a new array: correctlyAnsweredQuestion.

Similarly, if the response is incorrect then this array is itself stored in an array called incorrectlyAnsweredQuestion.

Redundant feature: In both cases we put an alert to the screen to indicate if the response to the question was correct or not. Arguably not required anymore due to question/answer summary printed to the html document at the end.
*/
for (let i = 0; i < questionAnswerPairs.length; i += 1) {
  questionResponse = prompt(questionAnswerPairs[i][0]);
  while (questionResponse === '') {
    alert("No response provided to the question! Please provide one to continue the quiz!");
    questionResponse = prompt(questionAnswerPairs[i][0]);
  }
  if (questionResponse.toLowerCase() === questionAnswerPairs[i][1].toLowerCase()) {
    correctAnswers += 1;
    correctlyAnsweredQuestion.push(questionAnswerPairs[i]);
    let correctMessage = alert(`Well done! ${questionAnswerPairs[i][1]} is the correct answer!`);
  } else {
      incorrectlyAnsweredQuestion.push(questionAnswerPairs[i]);
      let wrongMessage = alert(`Not quite, the answer was: ${questionAnswerPairs[i][1]}! Better luck new time!`);
  }
}

/* Following function returns lists of questions and associated answers. 
Originally only returned a list of questions as per class, but updated as I wanted the user to also see the answers for each question at the end.

This function creates two ordered lists, which are concatenated with list elements as the function runs.
The lists/arrays we pass to this function (correctlyAnsweredQuestion & incorrectlyAnsweredQuestion) appear to be two-dimensional (see other NOTE below). Hence the notation used in each for-loop conditional statement/initialisation block of refering to each array using two index values.

Each ordered list is opened, and populated with list elements according to how many elements are inside each array we pass to it.
If the user gets 2 questions wrong for example, then incorrectlyAnsweredQuestion[] contains two elements, each comprised of two elements, a question and an answer. This function would then create one ordered list comrpised of two questions, and one ordered list containing the two associated answers.
The i variable refers to the outer array, not the inner, as the for-loop needs to cycle through each sub array before pulling internal elements from each.
*/

function htmlList(list) {
  let orderedHtmlList = `Questions: <ol>`;
  for (let i=0; i<list.length; i += 1) {
    orderedHtmlList += `<li>${list[i][0]}</li>`;
  }
  orderedHtmlList += `</ol> Answers: <ol>`;
  for (let i = 0; i < list.length; i += 1) {
    orderedHtmlList += `<li>${list[i][1]}</li>`;
  }
  orderedHtmlList += `</ol>`;
  return orderedHtmlList;
}

/* NOTE: check up this part: 
using the toString method on correctlyAnsweredQuestion & incorrectlyAnsweredQuestion
   prints q & a's in a sequential order. How can we check if an array is multidimensional or not?
  print(correctlyAnsweredQuestion.toString());
print(incorrectlyAnsweredQuestion.toString());
*/


/*this string notififes of the number of correct answers achieved by the user, followed by two calls to the htmlList function. 
On each occasion the function is passed an array. Each call to the function creates two ordered lists.
Therefore the user recieves a score, then four ordered lists preceded by tags declaring what they are.
*/
resultsSummary = `<p>You got ${correctAnswers} question(s) right.</p>
                      <p>You got these questions correct:</p>
                            ${htmlList(correctlyAnsweredQuestion)}
                      <p>You got these questions wrong:</p>
                              ${htmlList(incorrectlyAnsweredQuestion)}`;

//prints the summary to the screen by calling the print function above.
print(resultsSummary);

correctlyAnsweredQuestion.push(questionAnswerPairs[i]);
//or
      incorrectlyAnsweredQuestion.push(questionAnswerPairs[i]);