Espero que la profesora aclare esa duda al final de la clase.

Because esperar que normally triggers the subjunctive when you are expressing a hope, wish, or expectation about something that has not happened yet.

• Espero que la profesora aclare... = I hope the teacher clarifies...
• Aclara would be the present indicative, used for facts:
  • La profesora aclara esa duda. = The teacher clarifies that doubt / question.

So after Espero que..., Spanish uses aclare.

Aclare is the present subjunctive of aclarar.

For regular -ar verbs, the present subjunctive endings are:

• yo: aclare
• tú: aclares
• él/ella/usted: aclare
• nosotros: aclaremos
• vosotros: aclaréis
• ellos/ellas/ustedes: aclaren

It comes from the yo form of the present indicative:

• present indicative yo: aclaro
• remove -o
• add subjunctive endings

So: aclaro → aclare

Here, aclarar means to clarify, to clear up, or to explain so that something becomes understood.

In this sentence, aclarar esa duda means something like:

• clear up that doubt
• clarify that question
• explain that uncertainty

It is very natural Spanish.

In Spanish, it is very common to use the definite article with a noun when it is the subject of the sentence.

So:

• La profesora aclare... is normal
• just profesora would usually sound incomplete here

This is different from English, where you can say the teacher or sometimes just teacher in special contexts. In Spanish, nouns usually need an article or another determiner unless they are being used in a special way.

Compare:

• La profesora llega tarde. = The teacher arrives late.
• Es profesora. = She is a teacher.

After ser for profession, the article is often dropped. But in your sentence, la profesora is the subject, so the article is expected.

Esa means that, while esta means this.

The basic contrast is:

• esta duda = this doubt / this question
• esa duda = that doubt / that question
• aquella duda = that doubt over there / that more distant doubt

In modern everyday Spanish, especially in many contexts, esa is a very normal general way to say that.

So esa duda means the speaker is referring to a specific doubt or question that is not being presented as this one right here.

Yes, its core meaning is doubt, but in Spanish it is also often used for a question, especially when the idea is that someone is uncertain about something.

So:

• pregunta = a question in a straightforward sense
• duda = a doubt, uncertainty, or question someone needs clarified

For example:

• Tengo una pregunta. = I have a question.
• Tengo una duda. = I have a question / I’m unsure about something.

In a classroom context, duda is very common and natural.

Al final de la clase means at the end of the class.

Al is the contraction of:

• a + el = al

So:

• al final = at the end

This is a fixed and very common expression.

Breakdown:

• al = at the / to the
• final = end
• de la clase = of the class

So literally: at the end of the class.

Yes, you can, if the context makes it clear who you mean.

Spanish often leaves out the subject when it is understood. So:

• Espero que la profesora aclare esa duda...
• Espero que aclare esa duda...

Both can be correct.

However, aclare could refer to she, he, you (formal), or even I in some contexts, so including la profesora makes the sentence clearer.

Not always. Esperar can mean different things depending on the structure:

• Espero que... = I hope that...
• Espero a la profesora. = I am waiting for the teacher.
• Espero una respuesta. = I am waiting for a reply / I expect a reply.

In your sentence, because it is Espero que + subjunctive, the meaning is clearly I hope.

It can change somewhat. Spanish word order is often more flexible than English.

Your sentence is very natural:

• Espero que la profesora aclare esa duda al final de la clase.

But you could also say:

• Espero que al final de la clase la profesora aclare esa duda.

Both are correct. The second version gives a little more emphasis to when it will happen.

Spanish often moves time expressions like al final de la clase around more freely than English does.

Because after verbs like esperar que, Spanish normally uses the present subjunctive to refer to a future action that is hoped for.

So even though the action is in the future, Spanish says:

• Espero que la profesora aclare...

not:

• Espero que la profesora aclarará... ← not correct here

This is very common in Spanish:

• Quiero que vengas. = I want you to come.
• Es posible que llueva. = It’s possible that it will rain.
• Espero que la profesora aclare... = I hope the teacher will clarify...

So the present subjunctive often covers what English expresses with will.