I had a similar issue with not being able to delete or reorder questions in the questionnaire, but I figured it out (I'm just posting in case anyone else has a similar problem). There are icons to delete or move questions, but they're really really small. So if you press ctrl and + a few times in your browser to make the text bigger, you can then see the icons and find the one for deleting.
Questionnaire (plugin)
Deleting questions in a questionnaire
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