How to say "I have something to ask you" or "I have something I need you to do please" in korean?
I'm teaching english to a couple of Koreans students and I have a questionnaire to ask them to fill out about English. But for the first part I need to know how do I say that. But the rest I know how to say and ask them.

Question

Answer

Here are strict translations of the two sentences.
(If talking to one person, use 'X 씨에게 / X 씨가' instead of 여러분에게 / 여러분이, where 'X' is the person's name)

1. I have something to ask you. 
=> 여러분에게 물어볼 게 있어요 or 여러분께 질문이 있어요 (I have question for you). 
2. I have something I need you to do please.
=> 여러분이 해야 [하셔야] 될 게 있어요. ('하셔야' is more respectful than '해야')

You could also say it a little differently in your situation.

1. 여러분이 설문지에 답변을 해 주셨으면 좋겠어요 (I would like to ask you to fill out a questionnaire).
2. 여러분이 (제게) 한 가지 해 주셨으면 좋겠어요 (I would like to ask you to do something for me).