koko ha kiken desu.

No. Japanese is normally written without spaces:

ここは危険です。

Spaces are often added in beginner materials to make the parts easier to see. In normal writing, you would not usually include them.

It is read:

ここはきけんです。
Romanization: koko wa kiken desu

A natural pronunciation is often close to koko wa kiken des because the u in です is often very light or devoiced.

When は is used as a particle, it is pronounced wa.

So in this sentence:

• ここ = here
• は = topic marker, pronounced wa

This is a standard spelling rule in Japanese. The character is still written は, even though it sounds like wa.

は marks the topic of the sentence.

So ここは means something like:

• as for here
• this place

The sentence is not just listing words; it is setting up ここ as the thing being talked about, then saying something about it: 危険です.

Japanese often leaves out words that are obvious from context.

In English, you might expect something like This place is dangerous. In Japanese, ここ already gives the location, and は marks it as the topic, so no extra word like it is needed.

That is very normal in Japanese.

危険 is read きけん.

It means danger or dangerous, depending on how it is used.

In this sentence, 危険 is being used as a predicate with です, so the whole meaning is is dangerous or is hazardous.

Because な is only used when a na-adjective directly modifies a noun.

For example:

• 危険な場所 = a dangerous place

But when 危険 comes before です at the end of the sentence, you do not use な:

• ここは危険です。

So:

• 危険な + noun
• 危険です at the end of a sentence

です makes the sentence polite and grammatically complete.

In this sentence, it works a lot like English is:

• ここは危険です。 = Here is dangerous / This place is dangerous

But it is better to think of です as a polite sentence-ending copula, not as a perfect one-to-one match for English is in every situation.

Yes, you could.

• ここは危険です。 = more formal, objective, sign-like, official
• ここは危ないです。 = more everyday, direct, conversational

危険です often sounds like something you might see on a warning sign or hear in an announcement.
危ないです can sound more immediate, like Watch out, this is dangerous.

Yes.

Polite:

• ここは危険です。

Plain/casual:

• ここは危険だ。

In conversation, people might also say:

• ここは危ない。

The version with です is polite and safe for learners to use.

A question:

• ここは危険ですか。 = Is this place dangerous?

A negative:

• ここは危険ではありません。 = This place is not dangerous.
• ここは危険じゃないです。 = This place isn’t dangerous. (less formal)

So the pattern is easy to reuse:

• A は B です。
• A は B ですか。
• A は B ではありません。