Ons werk daaraan.

• Ons = the subject, we
• werk = the verb, work
• daaraan = a prepositional form meaning on it / on that

So the structure is simply subject + verb + prepositional element.

Afrikaans often uses the simple present where English uses either the simple present or the present continuous.

So Ons werk daaraan can naturally mean:

• We work on it
• We are working on it

Afrikaans does not need a separate auxiliary like are here.

Usually, no. Afrikaans verbs are much simpler than English verbs in this way.

With most verbs, the present-tense form stays the same for all persons:

• ek werk
• jy werk
• hy werk
• ons werk
• julle werk
• hulle werk

So werk does not change to match ons.

Daaraan is a very common Afrikaans type of word called a pronominal adverb.

It is made from:

• daar = there / that
• aan = the preposition on / to / at, depending on the verb

With werk aan, the idea is work on something, so daaraan means on it / on that.

It usually refers to a thing, idea, project, problem, or situation already mentioned.

For things or ideas, Afrikaans often prefers daar- + preposition forms:

• daaraan
• daarop
• daarin
• daarmee

So daaraan is usually the most natural choice here.

Aan dit is possible in some contexts, especially for emphasis or contrast, but it is often less idiomatic in an ordinary sentence like this.

Also note:

• for people, you normally do not use daar- forms
  You would say things like aan hom, aan haar, aan hulle.

Because in Afrikaans, these daar- / hier- / waar- + preposition combinations are normally written together as single words.

For example:

• daaraan
• hieraan
• waaraan
• daarop
• hiermee

It is best to learn them as fixed forms.

In a normal main clause, Ons werk daaraan is the standard order.

But Afrikaans allows fronting for emphasis:

• Daaraan werk ons.

When that happens, the finite verb still stays in the second position, which is a very important Afrikaans word-order rule.

You also see this in questions:

• Werk ons daaraan?

And in subordinate clauses:

• ... dat ons daaraan werk

Yes, very often it is enough.

But if you want to make the ongoing/in-progress idea extra clear, Afrikaans often uses:

• Ons is besig om daaraan te werk.

That is closer to:

• We are busy working on it
• We are in the process of working on it

So:

• Ons werk daaraan = normal, simple, very natural
• Ons is besig om daaraan te werk = more explicitly progressive

Afrikaans usually uses a double negative:

• Ons werk nie daaraan nie.

The first nie comes after the verb phrase area, and the second nie comes at the end of the clause.

This double-nie pattern is one of the most important features of Afrikaans negation.

Yes. A very useful mini-set is:

• hieraan = on this
• daaraan = on that / on it
• waaraan = what ... on / that ... on / on which

Examples:

• Ons werk hieraan. = We are working on this.
• Ons werk daaraan. = We are working on it/that.
• Waaraan werk julle? = What are you working on?

Learning these together makes Afrikaans much easier.