eki no basu no noriba ga wakaranai ndesu ga, doko desu ka?

Because の is used to connect nouns, and Japanese often chains several nouns together.

Here, the phrase is built step by step:

• 駅の = of the station / at the station
• バスの乗り場 = bus boarding place
• So 駅のバスの乗り場 means something like the bus boarding place at the station

English usually avoids repeating of, but Japanese does this very naturally.

乗り場 is read のりば.

It comes from:

• 乗る = to ride / to get on
• 場 = place

So 乗り場 literally means a place for getting on. In this sentence, it means the place where you board the bus, such as:

• a bus stop
• a bus bay
• a boarding area
• a platform for buses

A related word is バス停, which means bus stop.
The difference is:

• バス停 = the bus stop itself
• バスの乗り場 = the place where you board the bus, often used in stations, terminals, or places with multiple bays

Because 分かる usually takes が, not を.

In standard Japanese, 分かる works more like:

• to be understood
• to be clear

So:

• 乗り場が分からない = the boarding place is not clear to me / I don't know where the boarding place is

This is one of those places where Japanese grammar does not match English very closely.

You may hear を分かる in casual speech in some contexts, but standard Japanese uses が分かる.

Both can relate to not knowing, but they are used differently.

• 知らない = I do not know as a fact
• 分からない = I do not understand / I can't tell / I'm not sure

For a location, 分からない is very natural because the speaker means:

• I can't figure out where it is
• I don't know how to identify it

So 乗り場が分からないんですが sounds natural and polite.

If you used 知らない, it would sound more like I have no knowledge of it, which is possible in some situations, but less natural here.

んです adds an explanatory or background-giving feeling.

It is a conversational form of のです.

So:

• 分からない = I don't know
• 分からないんです = The thing is, I don't know / I'm having trouble finding it

It often sounds softer and more natural when giving a reason before asking for help.

In this sentence, it helps set up the question politely:

• I can't figure out where the bus boarding place is, so... where is it?

The が here does not strongly mean but the way it often does in textbooks.

In real conversation, んですが is a very common way to introduce a request, question, or explanation politely. It often feels like:

• ...and so...
• ...so I wanted to ask...
• ...but...

So:

• 分からないんですが、どこですか？

means something like:

• I'm not sure where it is, so where is it?

It softens the question and makes it sound less direct.

You will also often hear んですけど used the same way.

It is omitted.

Japanese often leaves out subjects when they are obvious from context. In this sentence, I is understood naturally.

So:

• 乗り場が分からないんですが
  really means
• I don't know where the boarding place is

Even though there is no word for I, the listener understands that the speaker is talking about their own lack of knowledge.

This kind of omission is extremely common in Japanese.

The noun being asked about is left out because it was already mentioned.

The full idea is:

• 駅のバスの乗り場はどこですか

But since 駅のバスの乗り場 has just been mentioned, Japanese often drops it:

• どこですか = Where is it?

This is very natural. Japanese frequently avoids repeating information that is already clear.

Both are possible, but どこですか is shorter and very natural in conversation.

Compare:

• どこですか = Where is it?
• どこにありますか = Where is it located?

The second version is more explicit, but the first is often enough when asking about places such as:

• a stop
• a platform
• a counter
• a gate

So どこですか sounds normal and efficient here.

Yes, it is understandable and natural enough, especially in learner contexts.

However, in real life, native speakers might also say:

• 駅のバス乗り場
• 駅前のバス停 = the bus stop in front of the station
• バスターミナル = bus terminal

The best expression depends on what you mean exactly:

• a single bus stop near the station
• a bus boarding area attached to the station
• a larger terminal with many buses

So the phrase is fine, but there are other natural alternatives depending on the situation.

It is polite and appropriate for asking a stranger.

Why it sounds polite:

• です / か makes it polite
• んですが softens the request
• the wording is indirect rather than blunt

A very natural real-life version would often begin with すみません:

• すみません、駅のバスの乗り場が分からないんですが、どこですか。

That sounds courteous and normal.

A more formal version could be:

• 駅のバス乗り場が分からないのですが、どちらでしょうか。
• 駅のバス乗り場を教えていただけますか。

A casual version would be much shorter, such as:

• 駅のバス乗り場、どこ？

A rough breakdown is:

• 駅のバスの乗り場 = the bus boarding place at the station
• が = marks what is not understood
• 分からないんですが = I don't know / I'm not sure, and...
• どこですか = where is it?

So the sentence works like this:

• As for the bus boarding place at the station, I can't figure it out, so where is it?

Japanese often puts descriptive information before the noun, and then the main verb comes later. That is why the sentence can feel backward to English speakers at first.