Die meisie vir wie my pa wag, weet presies watter bus sy moet neem.

Because wag vir is the normal Afrikaans way to say wait for when you mention the person or thing being waited for.

• Ek wag. = I am waiting.
• Ek wag vir my pa. = I am waiting for my father.

So in your sentence, my pa wag is really my pa wag vir die meisie underneath, and that vir has to stay part of the structure.

Because die meisie is a person, and it is the object of the preposition vir.

In standard Afrikaans, when a relative clause involves a preposition, the preposition usually comes before the relative word:

• die man met wie ek praat = the man with whom I am speaking
• die meisie vir wie my pa wag = the girl for whom my father is waiting

A native English speaker often wants something like the girl my father is waiting for, with the preposition left at the end. Standard Afrikaans normally does not do that. It keeps vir together with wie.

Also:

• wie is used for people
• wat is not used here because wat would not carry the preposition in this structure

Because vir wie my pa wag is a subordinate clause, specifically a relative clause.

In Afrikaans subordinate clauses, the finite verb usually goes to the end:

• Main clause: My pa wag vir die meisie.
• Relative clause: die meisie vir wie my pa wag

So the word order changes because the clause is no longer standing alone; it is now describing die meisie.

The comma marks the end of the inserted relative clause.

The main clause is:

• Die meisie weet presies watter bus sy moet neem.

Into that, Afrikaans inserts the description:

• vir wie my pa wag

So the sentence becomes:

• Die meisie vir wie my pa wag, weet presies ...

That comma helps show that the sentence is now returning from the descriptive clause to the main statement.

Because weet is used for knowing a fact, answer, piece of information, or how to do something.

Here the girl knows which bus to take, so this is information. That is why Afrikaans uses weet.

Compare:

• Ek weet watter bus om te neem. = I know which bus to take.
• Ek ken die meisie. = I know the girl.

So:

• weet = know a fact / know that / know how / know which
• ken = know a person / be familiar with

Watter means which.

So:

• watter bus = which bus

In this sentence, watter bus sy moet neem means which bus she must/should take.

A learner may also hear watse in everyday speech, but watter is the standard written form.

Because this is an embedded question, not a direct question.

Direct question:

• Watter bus moet sy neem? = Which bus must/should she take?

Embedded question:

• Sy weet watter bus sy moet neem. = She knows which bus she must/should take.

In Afrikaans, embedded questions use subordinate-clause word order, so the verb does not come before the subject. Instead, the subject comes before the verb, and the verbal part moves toward the end.

Grammatically, moet often corresponds to must, but in real sentences it can also mean has to, needs to, or even should, depending on context.

So watter bus sy moet neem could be understood as:

• which bus she must take
• which bus she has to take
• which bus she should take

The exact nuance depends on the situation. Afrikaans moet is often a little broader in use than English learners first expect.

Because after a modal verb like moet, Afrikaans uses the bare infinitive.

So you say:

• sy moet neem
• ek kan gaan
• ons wil eet

not:

• sy moet te neem

This is similar to English, where you say must take, not must to take.

Because sy is the subject of moet neem.

• sy = she
• haar = her

So:

• sy moet neem = she must take
• ek sien haar = I see her

A small extra point: sy can also mean his in other contexts, which can confuse learners. But here it is clearly she, because it is followed by the verb moet.

Not in standard Afrikaans.

English can leave the preposition at the end:

• the girl my father is waiting for

Standard Afrikaans normally does not do that. The preposition must stay with the relative word:

• Die meisie vir wie my pa wag

So for a person after a preposition, preposition + wie is the pattern to learn.

Not in standard Afrikaans if you specifically mean which out of a set of choices.

• watter bus = which bus
• wat = what

So here watter is the natural choice because the girl knows which particular bus she should take, not just some general information about buses.

Yes, die meisie means the girl, so it normally refers to a specific girl.

That fits the relative clause well, because the sentence is identifying her more exactly:

• the girl for whom my father is waiting

If Afrikaans used 'n meisie, it would mean a girl, which would sound less specific:

• 'n Meisie vir wie my pa wag ... = a girl whom my father is waiting for ...

So die tells you the speaker has a particular girl in mind.