kokyuu no kakunin wo suru.

A natural breakdown is:

• 呼吸 = breathing / respiration
• の = links nouns, similar to of
• 確認 = confirmation / check
• を = marks the direct object
• する = to do

So the structure is:

• 呼吸の確認 = checking/confirmation of breathing
• 呼吸の確認をする = to do a breathing check

It is a very noun-heavy, procedural style of Japanese, which is common in instructions, manuals, and emergency/medical contexts.

Here, の connects 呼吸 and 確認.

So:

• 呼吸の確認 literally means confirmation of breathing
• more naturally in English: checking breathing

This use of の is very common in Japanese. It often links two nouns, where the first noun describes the second.

Other examples:

• 名前の確認 = confirmation of name
• 安全の確認 = safety check
• 体温の確認 = checking body temperature

Both are possible.

• 確認する = to confirm / to check
• 確認をする = to do a confirmation / to do a check

In many cases, they mean almost the same thing.

So:

• 呼吸の確認をする
• 呼吸の確認をする
• 呼吸の確認をする

and

• 呼吸の確認をする
• 呼吸の確認をする

Sorry—more simply:

• 呼吸の確認をする
• 呼吸の確認をする

Let me state it clearly:

• 確認する is a very common noun + する verb.
• Adding を makes the noun phrase more visibly the object of する.

In practical terms, 確認する and 確認をする are often interchangeable, though 確認する is usually a bit tighter and more direct.

を marks the whole noun phrase 呼吸の確認 as the object of する.

So it is not marking 呼吸 by itself.
It is marking:

• 呼吸の確認 = the breathing check

Then:

• 呼吸の確認をする = do the breathing check

That is why the sentence is not split like this:

• 呼吸を確認のする ✘

The phrase 呼吸の確認 has to stay together.

You can say that, and it is also natural.

Compare:

• 呼吸を確認する = check breathing
• 呼吸の確認をする = do a check of breathing

The difference is small, but the nuance is slightly different:

• 呼吸を確認する sounds more like directly checking breathing
• 呼吸の確認をする sounds a little more procedural or formal, like naming the action as a step

In first-aid instructions, manuals, and checklists, Japanese often prefers this kind of noun-based wording.

Japanese often omits the subject when it is obvious from context.

In an instruction like this, the implied subject is usually:

• you
• or the responder / person performing the procedure

So 呼吸の確認をする can be understood as:

• Check breathing
• You should check breathing
• Perform a breathing check

Japanese does this constantly. If the context makes the subject clear, it is usually left out.

する is the plain/dictionary form.

In instructional writing, Japanese often uses plain form for:

• headings
• procedure steps
• manuals
• checklists
• textbook examples

So 呼吸の確認をする。 can sound like a procedural step.

If you wanted a more polite version, you could say:

• 呼吸の確認をします。

If it were a command or instruction directed more clearly at someone, you might also see:

• 呼吸を確認してください。 = Please check breathing.

Yes, it is natural, especially in formal or instructional contexts.

Typical situations:

• first-aid procedures
• CPR instructions
• emergency response manuals
• training materials
• procedural checklists

It sounds more like a listed action or step than casual conversation.

In everyday conversation, someone might be more likely to say something like:

• 呼吸を確認して。 = Check their breathing.
• 呼吸があるか確認する。 = Check whether they are breathing.

They are read as:

• 呼吸 → こきゅう
• 確認 → かくにん
• する → する

So the full sentence is:

• こきゅう の かくにん を する。

In normal writing, it would usually appear without spaces:

• 呼吸の確認をする。

Those spaces are usually just for learners.

Normal Japanese writing does not normally put spaces between words like this. So a native-style version is:

• 呼吸の確認をする。

Textbooks and beginner materials sometimes add spaces to help learners see the parts more clearly.

By itself, 確認 is a noun meaning confirmation or check.

When combined with する, it functions like a verb:

• 確認する = to confirm / to check

This is a very common pattern in Japanese:

• 勉強 = study → 勉強する = to study
• 練習 = practice → 練習する = to practice
• 説明 = explanation → 説明する = to explain

So 確認 is a verbal noun, often called a suru-noun.

Yes, slightly.

• 確認 literally leans toward confirmation
• but in natural English, check is often the best translation in this kind of context

So in a medical or emergency instruction, check breathing usually sounds more natural than confirm breathing.

That said, the Japanese word 確認 still carries the idea of making sure something is true or present. So the underlying meaning is closer to verify/check/confirm.