SOLVED:
function copyAndSortNumbers(numbers) {
var oldArray = numbers;
var newArray = [].concat(oldArray);
return newArray.sort();
}

/ Do not modify code below this line /

const original = [1, 7, 3, 5];
const sortedCopy = copyAndSortNumbers(original);

console.log(original, '<-- should be [1, 7, 3, 5]');
console.log(sortedCopy, '<-- should be [1, 3, 5, 7]');

Do they want you to write your own sort function or call a sorting function?

Do they want you to do this:

function copyAndSortNumbers(numbers) {
    var newarr = [];
    for (...)
    {
        sorty code here
    }
    return newarr;
}

or do they want this?

function copyAndSortNumbers(numbers) {
    var newarr = numbers;
    newarr.sort()
}

If it's the 2nd part try:
https://www.w3schools.com/jsref/jsref_sort.asp