Ek weet nie of hulle reeds ontbyt bedien nie.

Because standard Afrikaans usually makes a sentence negative with nie ... nie.

In Ek weet nie of hulle reeds ontbyt bedien nie, the first nie comes after the finite verb in the main clause: weet nie. The second nie closes the negative sentence at the very end.

So the pattern is roughly:

Ek weet nie ... nie
= I do not know ...

Even though there is an of-clause in the middle, the negative frame still stretches to the end of the whole sentence.

Here of means whether or if in the sense of an indirect yes/no question.

So:

Ek weet nie of ... nie
= I don't know whether/if ...

This is not the same as the conditional if in a sentence like If it rains, we will stay home. In Afrikaans, that kind of if is usually as.

Also, of can mean or in other contexts, so learners often notice that and get confused. In this sentence, it definitely means whether/if.

Because of introduces a subordinate clause, and in Afrikaans subordinate clauses usually send the finite verb to the end.

So compare:

Hulle bedien reeds ontbyt.
= They already serve breakfast.

But after of:

... of hulle reeds ontbyt bedien
= ... whether they already serve breakfast

That verb-final order is very normal in Afrikaans after words like dat, omdat, as, terwyl, and of.

Reeds means already.

Yes, in many situations you can use al instead, and al is often more common in everyday speech.

So this sentence could also be:

Ek weet nie of hulle al ontbyt bedien nie.

Both are correct, but reeds can sound a little more formal or written.

Because meal words are often used without an article when you mean them in a general sense.

So Afrikaans commonly says:

ontbyt eet = eat breakfast
ontbyt bedien = serve breakfast

This is similar to English, where we usually say eat breakfast, not eat the breakfast, unless we mean a specific breakfast.

If you were talking about a particular breakfast, then an article could appear, for example die ontbyt.

Here it is a noun, meaning breakfast.

You can tell because the main verb in the clause is bedien = serve. So ontbyt is the thing being served.

Afrikaans ontbyt can also be a verb in other sentences, meaning have breakfast, for example:

Ons ontbyt vroeg.
= We have breakfast early.

But in your sentence, it is definitely a noun.

Because Afrikaans separates two kinds of know:

• weet = know a fact, piece of information, or answer
• ken = know a person, place, or something through familiarity

This sentence is about knowing information: whether they already serve breakfast. So weet is the right choice.

For comparison:

Ek weet dit.
= I know that.

Ek ken hom.
= I know him.

No, not in standard Afrikaans for this meaning.

After I don't know whether/if..., Afrikaans uses of, not as.

So the correct form is:

Ek weet nie of hulle reeds ontbyt bedien nie.

Use as for conditional or time-related if/when meanings, for example:

As hulle ontbyt bedien, sal ons daar eet.
= If they serve breakfast, we will eat there.

Here hulle means they.

It is the subject of the subordinate clause:

of hulle reeds ontbyt bedien
= whether they already serve breakfast

Afrikaans hulle can also mean them in other sentences, so context and word order matter. Here, because it comes before the verb bedien, it is clearly the subject.

The direct question would be:

Bedien hulle reeds ontbyt?
= Do they already serve breakfast?

That is useful to compare with the indirect version:

Ek weet nie of hulle reeds ontbyt bedien nie.
= I don't know whether they already serve breakfast.

So the indirect question uses of and puts the verb at the end, while the direct question starts with the verb.