sueop jeone jilmuneul memojange jeogeo duseyo.

전에 means before.

With a noun, you can use noun + 전에:

• 수업 전에 = before class
• 점심 전에 = before lunch

If you want to say before doing something with a verb, you usually use -기 전에:

• 먹기 전에 = before eating
• 자기 전에 = before sleeping

So here, 수업 전에 is simply before class.

The particles are showing different roles:

• 질문을: -을/를 marks the direct object, the thing being written down.
• 메모장에: -에 marks the place where something is written.

So:

• 질문을 적다 = write down a question / questions
• 메모장에 적다 = write it in/on a notepad

Together, 질문을 메모장에 적다 means write the question(s) in a notepad / notes app.

This is one of the most useful parts of the sentence.

• 적다 = to write down, jot down
• -아/어 두다 = do something in advance and leave it that way for later

So 적어 두세요 does not just mean write it down. It means something closer to:

• Please write it down beforehand
• Please make a note of it and keep it there for later

It suggests preparation. The idea is that you write the questions before class so they are ready when class starts.

적으세요 simply means please write it down.

적어 두세요 adds the meaning of doing it in advance or leaving it done for future use.

Compare:

• 질문을 적으세요. = Please write down the question(s).
• 질문을 적어 두세요. = Please write down the question(s) ahead of time and have them ready.

In this sentence, 적어 두세요 fits better because the action happens before class.

Because this is not a simple sequence of actions.

Here, 적어 두다 is a grammar pattern:

• verb stem + 아/어 두다

So:

• 적다 → 적어 두다

This pattern means do something and leave it done.

If you said 적고 두세요, that would sound like two separate actions:

• write it, and then put/leave it

That is not the intended structure here. The sentence uses the fixed auxiliary pattern -어 두다.

It can mean either one, depending on context.

메모장 can refer to:

• a physical memo pad / notepad
• a digital notes app on a phone, tablet, or computer

In everyday Korean, people often use 메모장 for both. So this sentence could mean:

• write your questions in a notebook
• write your questions in your notes app

The exact meaning depends on the situation.

Yes, it is a polite directive or request.

The ending -세요 is commonly used to tell someone to do something politely:

• 앉으세요. = Please sit down.
• 보세요. = Please look.

So 적어 두세요 is a polite way of saying:

• Please write them down in advance

It is very natural in instructions from a teacher, textbook, guide, or announcement.

It is polite, but still clearly tells the listener what to do.

The subject is omitted, which is very common in Korean.

The understood subject is you:

• (여러분은) 수업 전에 질문을 메모장에 적어 두세요.
• (You) write your questions down in a notepad before class.

Korean often leaves out subjects when they are obvious from context.

It can mean either.

Korean nouns usually do not have to show singular or plural unless it is important. So 질문을 can mean:

• a question
• questions

Context decides which is more natural. In this sentence, English often translates it as questions, because students may have more than one.

If the speaker really wanted to emphasize plural, they could say 질문들을, but that is not necessary here.

Yes, 질문을 메모장에 써 두세요 would also be natural.

The difference is small:

• 쓰다 = to write
• 적다 = to write down, note down, jot down

Because the sentence is about making a note before class, 적다 feels especially appropriate. It gives the sense of writing something down as a memo.

So both are possible, but 적어 두세요 fits the situation very well.