Meg tudja mondani, melyik peronról indul ez a járat?

Yes. Meg tudja mondani means can you tell (me) in a polite/formal way.

• tudja = you can / you know how to (formal you, or he/she depending on context)
• mondani = to say / to tell
• meg is a verbal prefix that often makes the action feel complete or successfully carried out

So Meg tudja mondani...? is a very common polite way to ask for information, similar to:

• Could you tell me...?
• Can you tell me...?

Without meg, the sentence would sound less natural here.

Because tudja is the formal form of you here.

Hungarian has informal and formal ways to say you:

• tudsz = you can (informal, singular)
• tudja = you can (formal, singular; literally the same form as he/she can)

So this sentence is polite, appropriate for asking a stranger, station staff, or an older person:

• Meg tudja mondani...? = formal/polite
• Meg tudod mondani...? = informal

Meg is a verbal prefix. In this sentence it suggests completion: not just say, but tell successfully / give the answer.

Compare the feeling:

• mondani = to say
• megmondani = to tell, to give the answer, to say it clearly/completely

That is why Hungarian often uses megmondani in questions like:

• Meg tudja mondani az időt? = Can you tell me the time?
• Meg tudod mondani, hol van...? = Can you tell me where ... is?

So meg does not translate as a separate English word here, but it is an important part of the natural Hungarian expression.

Good question. The full verb is indeed megmondani. But in Hungarian, verbal prefixes often separate from the verb when another element comes before the verb, especially with modal-like verbs such as tud.

So:

• dictionary form: megmondani
• in the sentence: Meg tudja mondani

This is normal Hungarian word order. The prefix meg moves in front of tudja, while mondani stays at the end of that verb phrase.

A very similar pattern:

• El tudok menni. = I can go.
• Be tudsz jönni? = Can you come in?

Melyik means which one.

Here it introduces the indirect question:

• melyik peronról = from which platform

Compare:

• mi? = what?
• melyik? = which one?
• milyen? = what kind of? / what is it like?

Examples:

• Mi ez? = What is this?
• Melyik vonat megy Budapestre? = Which train goes to Budapest?
• Milyen vonat ez? = What kind of train is this?

Since the speaker is choosing among possible platforms, melyik is the right word.

Because Hungarian uses case endings where English often uses prepositions.

peronról breaks down as:

• peron = platform
• -ról / -ről = from off / from

So:

• melyik peronról indul = departs from which platform

Hungarian expresses from the platform with the ending -ról, rather than a separate word like from.

Because of vowel harmony.

Hungarian suffixes often change depending on the vowels in the word:

• back-vowel words usually take -ról
• front-vowel words usually take -ről

peron has back vowels, so:

• peronról

Compare:

• asztalról = from the table
• székről = from the chair

This is a general Hungarian pattern you will see with many suffixes.

indul means depart, leave, or set off.

In transport contexts, it is very common for buses, trains, trams, and flights:

• A vonat hatkor indul. = The train leaves at six.
• Mikor indul a busz? = When does the bus leave?

So in your sentence:

• melyik peronról indul ez a járat = which platform this service departs from

Not exactly. Járat is more general. It means something like service, route, or scheduled departure.

Depending on context, it can refer to:

• a train service
• a bus service
• a flight
• another regular transport connection

So ez a járat means this service or this departure. In English, we might translate it more specifically depending on context, but Hungarian keeps it broader.

Because Hungarian normally uses the definite article with a noun after ez and az.

So the natural pattern is:

• ez a könyv = this book
• ez a vonat = this train
• ez a járat = this service

Literally, it looks like this the service, but that is just how Hungarian grammar works.

Because the rest of the sentence is an embedded question:

• Meg tudja mondani, ... ? = Can you tell me, ... ?

The part after the comma:

• melyik peronról indul ez a járat

is an indirect question, equivalent to which platform this service leaves from.

Hungarian commonly separates this kind of clause with a comma.

Yes, but it means something slightly different.

• Honnan indul ez a járat? = Where does this service depart from?
• Melyik peronról indul ez a járat? = Which platform does this service depart from?

So honnan asks more generally from where, while melyik peronról specifically asks from which platform.

Yes, you can think of it that way. Hungarian often leaves out things that are clear from context.

• Meg tudja mondani...? naturally means Can you tell me...?

If you wanted, you could make the to me explicit:

• Meg tudja nekem mondani...?

But in everyday speech, nekem is usually unnecessary here. The shorter version is very common and completely natural.