Elke kartondoos moet met die merkpen gemerk word.

In Afrikaans, elke means each or every, and it normally takes a singular noun.

So:

• elke kartondoos = every cardboard box
• not elke kartondose

This is similar to English, where we say every box, not every boxes.

Afrikaans often forms compound nouns by writing them as a single word.

Here:

• karton = cardboard
• doos = box
• kartondoos = cardboard box

This is very common in Afrikaans. English sometimes writes similar ideas as two words, but Afrikaans usually joins them:

• huisdeur = house door / front door
• skoolboek = school book
• merkpen = marker pen

So kartondoos is completely normal Afrikaans spelling.

Moet means must or has to.

In this sentence, it expresses obligation:

• Elke kartondoos moet ... gemerk word.
• Every cardboard box must be marked.

So the sentence is giving an instruction or requirement.

This is the passive voice in Afrikaans.

The pattern here is:

• moet
  • past participle + word

So:

• moet gemerk word = must be marked

Compare the active idea:

• Iemand moet elke kartondoos merk.
• Someone must mark every cardboard box.

Passive version:

• Elke kartondoos moet gemerk word.
• Every cardboard box must be marked.

Afrikaans often puts these verbal parts toward the end of the clause, especially when a modal verb like moet is present.

Gemerk is the past participle of merk.

• merk = mark
• gemerk = marked

The prefix ge- is very common in Afrikaans past participles.

Examples:

• maak → gemaak = made
• skryf → geskryf = written
• merk → gemerk = marked

In passive constructions, Afrikaans uses this participle:

• Die boks word gemerk.
• The box is being marked / is marked

So in your sentence, gemerk is there because the sentence is passive.

No. Afrikaans word here is a verb, not the English noun word.

In this sentence, word helps form the passive and means something like be / become in context.

So:

• gemerk word = be marked

A useful contrast is:

• is gemerk = is marked / has been marked depending on context
• word gemerk = is being marked / gets marked

With moet, the phrase becomes:

• moet gemerk word = must be marked

Met means with, and merkpen means marker pen or simply marker.

So:

• met die merkpen = with the marker pen

This tells you the instrument used to do the marking.

Compare:

• met 'n pen = with a pen
• met kryt = with chalk
• met die merkpen = with the marker pen

Die means the, while 'n means a/an.

So die merkpen refers to a specific marker pen, or one that is already understood in the situation.

• met die merkpen = with the marker pen
• met 'n merkpen = with a marker pen

If the instruction is about using one particular marker, die merkpen makes sense. If any marker would do, 'n merkpen could also be possible in a different sentence.

Afrikaans word order often differs from English, especially with:

• modal verbs like moet
• passive constructions
• participles at the end of the clause

English says:

• Every cardboard box must be marked with the marker pen.

Afrikaans says:

• Elke kartondoos moet met die merkpen gemerk word.

After moet, Afrikaans often sends the main verbal information toward the end:

• moet ... gemerk word

This is a very normal Afrikaans sentence pattern.

Yes, Afrikaans allows some flexibility.

For example, you could also hear:

• Elke kartondoos moet gemerk word met die merkpen.

That still means the same thing. However, Elke kartondoos moet met die merkpen gemerk word is a very natural and tidy order.

Both are grammatical, but the original version sounds especially standard in instructions.

One possible active version is:

• Iemand moet elke kartondoos met die merkpen merk.
• Someone must mark every cardboard box with the marker pen.

Here:

• iemand = someone
• merk = mark

The passive version removes the person doing the action and focuses on each cardboard box instead. That is why the passive is often used in instructions, rules, and procedures.