Die assessor gaan die waardasie en herstelkoste na.

Because the verb here is the separable verb nagaan, meaning to check, to examine, or to review.

In a main clause, Afrikaans often splits a separable verb:

• the conjugated part goes near the front: gaan
• the particle goes to the end: na

So:

• Die assessor gaan ... na. = The assessor checks/reviews ...

This is very similar to separable verbs in Dutch and somewhat like English phrasal verbs, though the word order is more fixed in Afrikaans.

Not by itself in this sentence.

Although gaan often means go, here it is part of the separable verb nagaan. So gaan ... na together means checks / examines / goes over.

So this sentence is not about physically going somewhere.

Compare:

• Hy gaan huis toe. = He goes home.
• Hy gaan die dokument na. = He checks the document.

No, not in this sentence.

Because of the final na, gaan is being used as part of nagaan, not as the future helper verb.

So:

• Die assessor gaan die waardasie en herstelkoste na.
  = The assessor checks/reviews the valuation and repair costs.

If you wanted is going to check, you would usually keep nagaan together as the infinitive:

• Die assessor gaan die waardasie en herstelkoste nagaan.
  = The assessor is going to check the valuation and repair costs.

That is a very important distinction.

The dictionary form is nagaan.

Some useful forms are:

• nagaan = to check / examine / review
• gaan ... na = present-tense main clause form
• het nagegaan = past tense
• om na te gaan = infinitive after om ... te

Examples:

• Die assessor gaan dit na. = The assessor checks it.
• Die assessor het dit nagegaan. = The assessor checked it.
• Die assessor wil dit nagaan. = The assessor wants to check it.
• Dit is belangrik om dit na te gaan. = It is important to check it.

Because die is the normal definite article in Afrikaans, and it is used for:

• singular nouns
• plural nouns
• all grammatical genders

Unlike languages such as German, Afrikaans does not change the based on gender.

So:

• die assessor = the assessor
• die waardasie = the valuation

This makes articles much simpler than in many other European languages.

Because one die can cover both nouns in a pair:

• die waardasie en herstelkoste

This means the valuation and repair costs.

Afrikaans, like English, often allows one article to apply to both coordinated nouns. You could also say:

• die waardasie en die herstelkoste

That is also grammatical, but the version with one die is very natural.

It is a compound noun:

• herstel = repair
• koste = costs / expenses

So herstelkoste literally means repair costs.

Afrikaans uses compound nouns very often, just like Dutch and German. English sometimes writes these as separate words, but Afrikaans commonly joins them into one word.

Other similar examples:

• motorongeluk = car accident
• versekeringsmaatskappy = insurance company

It is usually understood as costs or expenses, so in meaning it is plural or collective.

In English, we often say repair costs. Afrikaans uses koste in much the same way.

So herstelkoste is best understood as:

• repair costs
• the cost of repairs, depending on context

Yes, completely normal.

The sentence follows the standard main-clause pattern:

• Die assessor = subject
• gaan = finite verb in second position
• die waardasie en herstelkoste = object
• na = separable particle at the end

So the structure is:

Subject + finite verb + object + particle

That is exactly what you expect with a separable verb in a main clause.

It is a real Afrikaans word, and it is clearly a cognate/borrowing related to English assessor.

Afrikaans contains many words that look familiar to English speakers, especially in formal, legal, technical, or administrative language. Even when a word looks English, its grammar still follows Afrikaans rules.

So here:

• Die assessor = The assessor

is perfectly normal Afrikaans.

You would say:

om die waardasie en herstelkoste na te gaan

This is the infinitive pattern for separable verbs in Afrikaans:

• om + particle + te + verb

So for nagaan, the infinitive becomes:

• om ... na te gaan

Example:

• Die assessor moet die waardasie en herstelkoste nagaan.
  = The assessor must check the valuation and repair costs.

• Dit is nodig om die waardasie en herstelkoste na te gaan.
  = It is necessary to check the valuation and repair costs.