In two-part questions, should the examiner still ask the second part, for example "why", if the candidate has already answered this in their initial response?

Where questions have two parts and the teacher notes say to pause in between, it is not necessary to ask the second part of the question if the candidate has already replied in their initial answer. If you are satisfied that the candidate has responded fully to the question, including the second part, it is fine to move to the next question.