hubaeneun balpyohal ttaemada soni tteollindaeyo.

후배 means a junior: someone younger or lower in rank/experience than the speaker within a shared group, such as school, work, or an organization.

So depending on context, it could mean:

• a junior student
• a younger colleague
• a less experienced member

It does not by itself tell you gender. It can mean he or she.

는 is the topic marker, while 가 is the subject marker.

With 후배는, the sentence feels like:

• As for my junior...
• My junior, when giving presentations, ...

This sets 후배 up as the topic of discussion.

If you said 후배가 발표할 때마다 손이 떨린대요, it would sound a bit more like you are simply identifying the junior as the subject, possibly with more focus on who it is.

So:

• 후배는 = topic, often more natural in conversational explanation
• 후배가 = subject focus

Both can be grammatical, but 후배는 is very natural here.

발표할 때마다 means every time they give a presentation.

Breakdown:

• 발표하다 = to present / give a presentation
• 발표할 때 = when presenting
• -마다 = every / each / whenever

So 때마다 literally means every time when...

Compare:

• 발표할 때 = when giving a presentation
• 발표할 때마다 = every time they give a presentation

The -마다 adds the repeated, habitual meaning.

In Korean, the normal pattern for when doing something is verb stem + -ㄹ/을 때.

So:

• 발표하다 → 발표할 때 = when presenting

Even though -ㄹ/을 often looks like a future marker in other contexts, in -ㄹ/을 때 it commonly just means when one does X.

So 발표할 때 is the standard, natural form here.

발표하는 때 is not the usual everyday way to say this in this structure.

Because 떨리다 is usually used as an intransitive verb meaning something like:

• to tremble
• to shake
• to quiver

So the hands themselves are treated as the grammatical subject:

• 손이 떨리다 = the hands shake / the hands tremble

That is why you use 이/가, not 을/를.

This is a very common Korean pattern with body parts:

• 다리가 아파요 = my leg hurts
• 심장이 떨려요 = my heart trembles
• 손이 떨려요 = my hands shake

English often says I am nervous, but Korean often describes the physical symptom instead.

떨린대요 is a contracted conversational form of 떨린다고 해요.

Formation:

• 떨리다 = dictionary form
• 떨린다 = plain declarative form
• 떨린다고 해요 = says that the hands shake / I hear that the hands shake
• 떨린대요 = contracted spoken form of 떨린다고 해요

So 떨린대요 often means:

• they say their hands shake
• I hear that their hands shake
• apparently their hands shake

It is a reported-speech form.

Not always. It is used for reported speech, and that can come from different sources.

In this sentence, it could mean:

1. The junior says their hands shake every time they present.
2. The speaker is relaying information they heard from someone else: I hear that the junior’s hands shake...

So -대요 does not always mean vague rumor. It can also be a casual way of reporting what someone said.

The exact nuance depends on context.

Often, yes.

Literally, 손이 떨리다 means one’s hands tremble, but in context it usually implies nervousness, fear, pressure, or stage fright.

So this sentence can naturally suggest:

• the junior gets nervous during presentations
• the junior’s hands shake whenever they present

Korean often describes the physical reaction instead of using a direct adjective like nervous.

It is polite conversational speech.

The 요 makes it polite.
The -대요 part is casual-spoken in style, softer and more natural in everyday conversation than something more formal like:

• 떨린다고 합니다 = more formal
• 떨린대요 = natural spoken polite style

So the whole sentence sounds like something you might say in normal polite conversation, not in a very formal report.

Yes.

Korean does not usually mark gender in a sentence like this unless it is specifically stated elsewhere.
So 후배는 발표할 때마다 손이 떨린대요 can mean:

• My junior says his hands shake whenever he presents
• My junior says her hands shake whenever she presents

You need context to know which one.

Because Korean very often leaves possession implied when it is obvious from context.

So:

• 후배는 ... 손이 떨린대요

naturally means:

• the junior’s hands shake

Even though Korean does not explicitly say 후배의 손이, the listener understands that the hands belong to the junior.

Korean often avoids unnecessary possessives when the owner is already clear from the sentence.