Here are some stock phrases you can use as an armour when you face any problem in IELTS Speaking interview...First of all, practise yourself a lot as this could be one of the most important exams your life and try to avoid this kind of situations when you don't understand ( in fact they are going to use only those words which are internationally valid and mostly easily understandable) or miss the examiner, but even tough if it happens like this just use the words I have provided here....Hope this will help.
1) If you need time to collect your thoughts use expressions (sparingly) like:
'That's a good question...',
'Well, let me think ...’,
'Well, It's quite difficult for me to say.....',
It is bit difficult for me to predict about the future, but looking at the current scenario I can say that........( when you are asked to say something about the future of something)
"Sorry but could you explain what you mean by ........"
"I haven't come across that word/expression before. Could you explain what you mean?"
"Excuse me, I didn't quite catch that. Could you say that again?"
"I'm sorry, but would you mind repeating that?"
"Do you mean ........"
"When you say ........, do you mean/are you asking........?