@sdfarq.sf

请你说慢一点儿 = please speak more slowly.

请你再说一遍 = please say that again.

The second quotation you used is grammaticaly incorrect. It appears that you are using English grammar in Chinese: "sorry, what did you say?" Not to worry, we all do it. Also, you don't need to add the partical "吗" when using "什么" in a question.