What should you do if you don't understand a question in the speaking test? Here are my tips:
In part 1, the examiner is not allowed to help you, but he/she can repeat the question. Just say: "Sorry, can you repeat the question please?" If you still don't understand the second time, try to say something related to the topic or any of the words that you heard. Try your best, then focus on the next question.
You are given a task card with the question written on it, so you shouldn't have any problems in this part. If there is a word that you don't understand on the task card, don't ask the examiner - he/she is not allowed to help.
In this part of the test, the examiner is allowed to rephrase the question. If you don't understand, just say something like: "Sorry, can you explain that question in a different way please?"