hensokuki wo kakuninsuru.

It is read:

へんそくきを かくにんする
hensoku-ki o kakunin suru

• 変速機 = へんそくき
• を = pronounced o
• 確認する = かくにんする

In natural speech, を may sound closer to o than wo.

を marks the direct object of the verb.

So in 変速機を確認する:

• 変速機 = the thing being checked
• 確認する = to check / confirm
• を = shows that 変速機 is what the checking is being done to

So the structure is basically:

[thing] を [verb]
gearbox/transmission + object marker + check

The dictionary form is very common in:

• manuals
• instructions
• labels
• checklists
• written procedures
• technical writing

So 変速機を確認する。 can sound like a manual instruction such as Check the transmission.

If you wanted a more polite full sentence in conversation, you might say:

• 変速機を確認します。
• 変速機を確認してください。 = Please check the transmission.

Yes. Japanese often leaves out the subject when it is obvious from context.

In a manual or checklist, the implied subject is often something like:

• you
• the worker
• the mechanic
• or just an impersonal instruction

So even without saying you, 変速機を確認する。 works naturally as an instruction.

It is a real and correct word, but it sounds somewhat technical.

変速機 means transmission or gearbox, especially in mechanical or automotive contexts.

In everyday conversation, people may also say things like:

• ミッション
• トランスミッション
• sometimes ギア in looser speech, depending on what exactly they mean

But in manuals, inspections, and technical documents, 変速機 is very natural.

確認する is more specific than 見る.

• 見る = to look at, to see
• 確認する = to check, verify, make sure

So 変速機を見る could just mean look at the transmission.
But 変速機を確認する suggests a more purposeful check, such as making sure it is functioning correctly or checking its condition.

This makes 確認する especially common in work instructions and safety procedures.

It sounds:

• direct
• procedural
• technical
• like an instruction or checklist item

It does not sound especially emotional or conversational. It sounds like something you would read in:

• an inspection manual
• maintenance steps
• a training document
• a work order

So the tone is closer to Inspect/Check the transmission than casual conversation.

Normally, standard Japanese is written without spaces:

変速機を確認する。

If you see spaces, they are often added for:

• learners
• readability
• word separation in teaching materials

So the spaces are not part of normal Japanese spelling; they are just a learning aid.

A simple breakdown is:

• 変速機 = transmission / gearbox
• を = object marker
• 確認する = to check / confirm

So the pattern is:

noun + を + suru-verb

This is a very common pattern in Japanese.
Other examples:

• 書類を確認する = check the documents
• 内容を確認する = confirm the contents
• 安全を確認する = confirm safety

Yes. The exact English translation depends on context.

確認する can mean:

• to check
• to confirm
• to verify
• to make sure

In this sentence, because 変速機 is a machine part, check is usually the most natural translation.
In another context, such as 予定を確認する, it might be better translated as confirm.

Yes, if you are directly telling someone please check the transmission, then:

変速機を確認してください。

is more natural and polite.

Compare:

• 変速機を確認する。 = checklist/manual style, plain instruction
• 変速機を確認します。 = polite statement: I will check / we check
• 変速機を確認してください。 = please check it

So the best version depends on whether the sentence is a manual entry, a statement, or a request.

It is built from:

• 確認 = confirmation / checking
• する = to do

Together, they function as the verb to confirm / to check.

This is called a suru verb. Many Japanese verbs work this way, especially formal or technical ones.

Other examples:

• 点検する = to inspect
• 修理する = to repair
• 運転する = to drive / operate

So 確認する is grammatically a noun + する, but you can treat it as one verb when learning.