Very close, try:
questionText = questionText.replace(/[0-9]/g, '');
replace
doesn't work on the existing string, it returns a new one. If you want to use it, you need to keep it!
Similarly, you can use a new variable:
var withNoDigits = questionText.replace(/[0-9]/g, '');
One last trick to remove whole blocks of digits at once, but that one may go too far:
questionText = questionText.replace(/d+/g, '');
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