The answer to this is again - it depends on the part of the exam you are in. In the first part of the speaking test, you can ask for the examiner to repeat the question. At the same time, in part 2, you can ask for the clarification of the question you don't understand during the 1 minute of preparation time that it gets. In part 3 of the Speaking test, the examiner can paraphrase the question into a simpler language. Also do keep in mind that you should ask the question to the examiner leading with the parts that you do understand and letting them know what you think about the parts that you don't understand.