Ik wacht op spoor vier op de trein naar Amsterdam.

Because the two ops do different jobs.

• wachten op is a fixed combination meaning to wait for
• op spoor vier gives the location: on/at platform four

So in:

Ik wacht op spoor vier op de trein naar Amsterdam

the first idea is where you are, and the second is what you are waiting for.

Literally, spoor means track. But at a train station, Dutch often uses spoor where English would normally say platform.

So:

• spoor vier = the departure point numbered 4
• in natural English, this is usually platform 4

You may also hear perron vier, but spoor 4 is extremely common in station language, signs, and announcements.

With numbered places like platforms, rooms, buses, and trains, Dutch often leaves out the article.

So Dutch normally says:

• op spoor vier
• in kamer drie
• met bus 12

not:

• op het spoor vier

If you were talking about the track in a general sense, then you would use the article:

• het spoor is nat = the track is wet

But with a number label, article omission is normal.

Because in Dutch, wachten op means to wait for someone or something.

Examples:

• Ik wacht op de trein = I am waiting for the train
• Zij wachten op hun vriend = They are waiting for their friend

If you just say Ik wacht, it means I am waiting, but it does not say what for.

This is just something you have to learn with the verb:

• wachten op iets/iemand

A useful contrast:

• wachten op = wait for
• wachten tot = wait until

Example:

• Ik wacht tot acht uur = I’m waiting until eight o’clock

Because naar is the normal preposition for a destination.

So:

• de trein naar Amsterdam = the train to Amsterdam
• de bus naar Utrecht = the bus to Utrecht
• een vlucht naar Londen = a flight to London

In this sentence, naar Amsterdam describes which train it is: the one whose destination is Amsterdam.

Because city names in Dutch normally do not take an article.

So you say:

• naar Amsterdam
• in Rotterdam
• uit Utrecht

not:

• naar het Amsterdam

This is similar to English, where you usually say to Amsterdam, not to the Amsterdam.

Yes. That is also possible.

Both versions are understandable:

• Ik wacht op spoor vier op de trein naar Amsterdam
• Ik wacht op de trein naar Amsterdam op spoor vier

The difference is mainly emphasis and information order.

• If you say op spoor vier earlier, you highlight the location sooner.
• If you say op de trein naar Amsterdam earlier, you highlight what you are waiting for sooner.

Dutch is fairly flexible here, especially with prepositional phrases like these.

Yes, in many contexts it is.

Dutch simple present often covers both:

• I wait
• I am waiting

So:

• Ik wacht op de trein can mean I wait for the train or, more naturally in context, I’m waiting for the train

If you really want to stress that the action is going on right now, Dutch can also use a progressive construction, for example:

• Ik ben op de trein aan het wachten
• Ik sta op de trein te wachten

But in normal speech, plain Ik wacht is very common and completely natural.

It is understandable and acceptable, but many speakers might more often say:

• Ik wacht op de trein naar Amsterdam op spoor vier

That version may feel a little clearer because the phrase op de trein stays closer to wacht.

In spoken Dutch, you might also hear something like:

• Ik sta op spoor vier op de trein naar Amsterdam te wachten

That sounds a bit more conversational.

So the original sentence is fine, but it is not the only natural option.

Both are possible, depending on context.

• In normal prose, writing the number as a word, vier, is common.
• On signs, timetables, and station displays, you will usually see spoor 4

So:

• spoor vier = normal written-out form
• spoor 4 = very common practical/station form

Both mean exactly the same thing.