Vurderingen bygger på faktumet og beviset.

Because vurderingen is the definite singular form of vurdering.

• en vurdering = an assessment / an evaluation
• vurderingen = the assessment / the evaluation

In Norwegian, the definite article is often attached to the end of the noun instead of being a separate word.

Norwegian usually puts the onto the noun as an ending.

So:

• vurdering = assessment
• vurderingen = the assessment
• faktum = fact
• faktumet = the fact
• bevis = proof / evidence
• beviset = the proof / the evidence

You can sometimes also use den/det/de with a definite noun, but that is usually for extra emphasis or when an adjective is involved.

Bygger på literally means builds on, but in this kind of sentence it usually means is based on or rests on.

So even though the Norwegian uses a form that looks more active, the natural English meaning is often:

• Vurderingen bygger på ... = The assessment is based on ...

This is a very common Norwegian expression.

Norwegian often expresses this idea more directly with bygge på.

Compare:

• Vurderingen bygger på faktumet og beviset.
• more literally: The assessment builds on the fact and the evidence.
• natural English: The assessment is based on the fact and the evidence.

Norwegian can also say:

• Vurderingen er basert på ...

That is also correct and often feels slightly more formal or closer to English wording.

Because bygge på is the normal fixed expression for to be based on / to build on.

Prepositions often have to be learned together with the verb. In this case, på is just the standard choice.

Examples:

• Teorien bygger på forskning. = The theory is based on research.
• Avgjørelsen bygger på loven. = The decision is based on the law.

Because both nouns are neuter nouns.

Their indefinite forms are:

• et faktum
• et bevis

For many neuter nouns, the definite singular ending is -et:

• et faktum → faktumet
• et bevis → beviset

By contrast, many masculine/feminine nouns take -en or -a in the definite singular.

Because faktumet is singular definite: the fact.

• et faktum = a fact
• faktumet = the fact

Fakta usually means facts or factual information.

So the difference is roughly:

• faktumet = one specific fact
• fakta = facts in general, or multiple facts

Depending on context, many Norwegians might actually say fakta if they mean a body of factual information rather than one single fact.

That is a very common learner question. In Norwegian, bevis can be used more countably than English evidence.

So:

• et bevis = a piece of evidence / a proof
• beviset = the evidence / the proof
• bevis can also be plural depending on context

English often prefers evidence as an uncountable noun, but Norwegian is more comfortable treating bevis as a countable item.

Yes, it is grammatically correct and understandable.

That said, depending on context, some speakers might prefer slightly different wording, for example:

• Vurderingen bygger på fakta og bevis.
• Vurderingen er basert på fakta og bevis.

Your sentence sounds most natural when you mean one particular known fact and one particular known piece of evidence.

The basic structure is:

• Vurderingen = subject
• bygger = finite verb
• på faktumet og beviset = prepositional phrase

So the sentence follows normal main-clause word order.

A useful rule in Norwegian is that the finite verb usually comes second in main clauses. Here, the subject comes first, so the verb comes right after it.

• Vurderingen bygger på faktumet og beviset.

If another element were moved to the front, the verb would still stay in second position.