建议你用的句子：

Could you please rephrase that question/topic?　　　
　　
I'm not exactly sure what you mean　...
　　
I'm not exactly sure how to answer that question, but (perhaps)　...
　　
That's a rather difficult question, but (maybe)...
　　
I'm sorry, but I don't know much about　...　　　　　　　　　　　
　　
However, it might be possible that　...　
　　
Maybe I can answer your question by telling you about a personal experience I had.　
　　
That's an interesting question　...　　　　　　　　　　　　
　　
Let me see. Well, I suppose that　...
　　
Well, I think there are 2 (or 3 or more) reasons:　　　　　　　　　　　
　　
First, ... Second, ... Finally,　...
　　
In my opinion there are three ways of looking at it:　　　　　　　　
　　
First of all, ... Next, ... Then, ...
　　
Have I given you enough information?　
　　
Would you like me to tell you more about...?
　　
Is that all you'd like to know?
　　
I'm afraid that's about as much as I know.
　　
I think that's about it.
　　
I can't think of anything else right now...