Ele conhece o inimigo.

Conhece is the third-person singular present tense form of conhecer.

So:

• eu conheço = I know
• você / ele / ela conhece = you / he / she knows
• nós conhecemos = we know
• eles / elas conhecem = they know

In Ele conhece o inimigo, conhece matches ele.

Portuguese usually separates two ideas that English often expresses with to know:

• conhecer = to know someone/something through familiarity, acquaintance, or experience
• saber = to know a fact, information, or how to do something

So:

• Ele conhece o inimigo = he is familiar with / knows the enemy
• Ele sabe a resposta = he knows the answer
• Ela sabe nadar = she knows how to swim

A learner often wants to translate English know with just one verb, but Portuguese normally does not work that way.

O is the masculine singular definite article, meaning the.

So:

• o inimigo = the enemy
• um inimigo = an enemy

Portuguese uses articles very naturally and often more consistently than English. In this sentence, o inimigo refers to a specific enemy, or at least to the enemy as an identifiable person/group in context.

Often, ele is not required if the context already makes the subject clear.

Portuguese is a language that frequently allows the subject pronoun to be omitted:

• Ele conhece o inimigo.
• Conhece o inimigo.

Both can work, but there is a difference in feel:

• Ele conhece o inimigo sounds more explicit.
• Conhece o inimigo depends more on context.

Speakers may keep ele for clarity, contrast, or emphasis.

Inimigo means enemy.

It can refer to:

• a literal enemy in war or conflict
• a personal enemy
• a figurative opponent

Examples:

• O inimigo atacou. = The enemy attacked.
• Ele é meu inimigo. = He is my enemy.

Here it is masculine singular because the word is o inimigo.

In Brazilian Portuguese, conhece is approximately:

ko-NYEH-see

A more IPA-like version is:

[koˈɲɛsi]

The important part is nh, which sounds like the ny in canyon or like Spanish ñ.

So:

• co
• nhe
• ce

not like English con-he-see

A rough Brazilian Portuguese pronunciation is:

EH-lee ko-NYEH-see oo ee-nee-MEE-goo

A more phonetic approximation:

[ˈɛli koˈɲɛsi u iniˈmigu]

A few notes:

• Ele sounds like EH-lee
• conhece has that ny sound: ko-NYEH-see
• o is usually a short oo sound in Brazilian Portuguese
• inimigo stresses MI: ee-nee-MEE-goo

In natural speech, o inimigo may flow together smoothly.

Because o here is just the article the, followed directly by the noun inimigo.

Contractions in Portuguese usually happen when a preposition combines with an article, for example:

• de + o = do
• em + o = no
• a + o = ao

But here there is no preposition, just:

• o inimigo = the enemy

So no contraction is needed.

No. This is the normal, neutral word order in Portuguese:

Subject + Verb + Object

• Ele = subject
• conhece = verb
• o inimigo = object

So the structure is very similar to English.

Yes, depending on context.

With people, conhecer often means:

• to know someone
• to be acquainted with someone
• to have met someone

So Ele conhece o inimigo could suggest that he is familiar with who the enemy is, perhaps because he has encountered him before.

Context decides how strong that sense is.

You add não before the verb:

Ele não conhece o inimigo.
= He does not know the enemy.

That is the normal way to make a sentence negative in Portuguese.

In Brazilian Portuguese, you can often keep the same word order and let your intonation show that it is a question:

Ele conhece o inimigo?

In writing, the question mark makes it clear.

You could also ask with extra words in a larger context, but the simplest yes/no question is just the same sentence with question intonation.

You would change the subject and the verb form:

• Eu conheço o inimigo. = I know the enemy.
• Ela conhece o inimigo. = She knows the enemy.
• Eles conhecem o inimigo. = They know the enemy.
• Elas conhecem o inimigo. = They know the enemy.

Notice:

• ele / ela conhece
• eles / elas conhecem
• eu conheço

Not always, but very often when a specific noun is meant.

Compare:

• Ele conhece o inimigo. = He knows the enemy.
• Ele conhece um inimigo. = He knows an enemy.
• Ele conhece inimigos. = He knows enemies.

Portuguese tends to use articles naturally, and learners often need time to get used to when they sound expected.

Yes. The feminine form is inimiga.

So:

• o inimigo = the male enemy / the enemy
• a inimiga = the female enemy

Example:

• Ele conhece a inimiga. = He knows the female enemy.

And the plural forms are:

• os inimigos
• as inimigas

Normally, ele means he.

In some contexts, Portuguese can use ele/ela for things that have grammatical gender, but in a basic sentence like this, a learner should understand ele as he unless context clearly shows otherwise.