Si alguien es maleducado en una reunión, la profesora lo nota enseguida por su actitud.

Because si without an accent means if.

• si = if
• sí = yes

So Si alguien es maleducado... means If someone is rude..., not Yes, someone is rude...

This sentence expresses a general truth or a habitual result:

Si + present, present

So:

• Si alguien es maleducado... = If someone is rude...
• ...la profesora lo nota enseguida = ...the teacher notices it right away

This is a very common pattern in Spanish for things that generally happen.

Spanish normally uses ser with adjectives like maleducado when describing someone's behaviour or character as rude / ill-mannered.

• es maleducado = is rude / is ill-mannered

Using estar here would sound unnatural in standard Spanish. Maleducado is usually treated as a characteristic or judgment about behaviour, so ser is the normal choice.

Maleducado means rude, ill-mannered, or literally something like badly brought up.

It changes for gender and number:

• maleducado = rude (masculine singular)
• maleducada = rude (feminine singular)
• maleducados / maleducadas = rude (plural)

Here it appears in the masculine singular because alguien often takes masculine singular agreement when the gender is unspecified.

It means in / at a meeting.

Spanish often uses en for events and situations where English might say at:

• en una reunión = at a meeting
• en clase = in class / at school lessons
• en una fiesta = at a party

So although en often translates as in, here the natural English meaning is at a meeting.

Spanish often uses the definite article with professions or roles when talking about a specific person as the subject of a sentence.

So:

• La profesora lo nota = The teacher notices it

But after ser, the article is usually dropped:

• Es profesora = She is a teacher

So la profesora is normal here because it means the teacher, a specific person.

No. Here nota is a verb: the third-person singular of notar.

• notar = to notice
• la profesora nota = the teacher notices

As a noun, nota usually needs an article or another determiner:

• una nota = a note
• la nota = the grade / the note

So in this sentence, nota is definitely the verb.

Here lo refers to the idea that the person is being rude — basically it or that.

So:

• la profesora lo nota = the teacher notices it / notices that

Spanish often uses lo to refer to a whole situation, fact, or quality that has just been mentioned.

In other words, she notices the rudeness or the fact that the person is rude.

Because lo here is best understood as referring to the fact or behaviour, not directly to a female person.

So it works like:

• She notices it
• She notices that

This lo is not really about biological gender here. It is a very common Spanish way to refer back to a whole idea.

If you were clearly referring to a female person as the direct object, then la could be used:

• La profesora la nota enseguida = The teacher notices her right away

But that is not the most natural reading of this sentence.

Because object pronouns normally go before a conjugated verb in Spanish.

So:

• lo nota
• la ve
• me escucha

This is the standard position with normal finite verbs.

Pronouns can attach to other forms, such as:

• infinitive: va a notarlo
• gerund: está notándolo
• affirmative command: nótalo

But with a regular conjugated verb like nota, the pronoun goes before it: lo nota.

Enseguida means right away, immediately, or straight away.

It is a very common everyday word in Spanish.

So:

• lo nota enseguida = she notices it right away

It is close in meaning to inmediatamente, but enseguida often sounds a bit more natural and conversational.

It means from their attitude, by their attitude, or because of their attitude, depending on how you translate it.

Here por expresses the clue, cause, or evidence that lets the teacher notice the rudeness.

So the idea is:

• the teacher notices it
• because of / from the person’s attitude

Because actitud is singular, so the possessive must also be singular:

• su actitud = his attitude / her attitude / their attitude

In Spanish, su agrees with the thing possessed, not with the owner.

So even if the owner is understood as someone of unknown gender, Spanish still uses:

• su actitud because actitud is singular

Yes. Alguien means someone / somebody, and it can refer to a person of any gender.

When the gender is unknown or not specified, Spanish often defaults to masculine singular in agreement:

• alguien es maleducado

If you wanted, you could rephrase to make the person explicitly feminine:

• Si una chica es maleducada...

But alguien itself is gender-neutral in meaning.

Yes, absolutely.

• Si alguien es maleducado... = If someone is rude...
• Si una persona es maleducada... = If a person is rude...

The version with alguien sounds a bit more natural and general in everyday Spanish.
With una persona, the adjective would usually agree with persona, which is feminine:

• una persona maleducada

So both are correct, but alguien is more idiomatic here.