E.g. for "What is your role?" for attendees to select:
other (please specify)
This is super simple:
Add a new question
Select the question type: "Dropdown with text (multi-line)"
Add the question text: "What is your role? If other please specify in free text below"
When people select other and specify their role in the free text box, it will appear as below. And will be perfectly categorised for you on your feedback dashboard and the spreadsheet.