Eu entendo a questão.

Yes. In Brazilian Portuguese, subject pronouns are often omitted when the verb form already makes the subject clear.

So:

• Eu entendo a questão.
• Entendo a questão.

Both are natural and correct.

Including eu can add emphasis, contrast, or clarity. For example, Eu entendo a questão, mas ele não gives extra stress to I.

Entendo is the first-person singular form of the verb entender, meaning to understand.

It is in the present indicative:

• eu entendo = I understand
• você entende = you understand
• ele/ela entende = he/she understands
• nós entendemos = we understand
• vocês entendem = you all understand
• eles/elas entendem = they understand

So in this sentence, entendo tells you the subject is I.

Here, a is the definite article meaning the.

• a questão = the issue / the question / the matter

Portuguese uses articles more often than English does, so where English might sometimes say I understand this issue or even just I understand the issue, Portuguese very naturally uses a here.

Also, questão is a feminine noun, so it takes a, not o.

It can mean more than just question.

Depending on context, questão can mean:

• question
• issue
• matter
• point
• problem

So Eu entendo a questão could mean:

• I understand the question.
• I understand the issue.
• I understand the matter.

The exact meaning depends on the situation.

Because grammatical gender in Portuguese is part of the noun itself, and questão is simply a feminine noun.

That is why you say:

• a questão
• not o questão

This is something you generally have to learn with the noun. The ending -ão does not always mean masculine. For example:

• o coração = the heart
• a decisão = the decision
• a questão = the issue/question

So it is best to memorize nouns together with their article.

A simple approximate guide:

• entendo ≈ en-TEN-doo
• questão ≈ kes-TAWN with a nasal ending

A few details:

• In entendo, the stress is on ten.
• In questão, the stress is on the last syllable: tão.
• The ão sound is nasal and very common in Portuguese. It does not sound exactly like any normal English vowel.

A rough pronunciation of the whole sentence is:

• eh-oong en-TEN-doh ah kes-TAWng

That is only an approximation, but it helps as a starting point.

This is the most neutral word order in Portuguese:

• subject + verb + object

So:

• Eu = subject
• entendo = verb
• a questão = object

You can change the word order in some contexts, but the basic form is the most common and natural for learners.

For example:

• A questão eu entendo.

This is possible, but it sounds marked, as if you are emphasizing the issue specifically.

They are close in meaning, and both can mean to understand.

• entender is very common and everyday.
• compreender can sound a little more formal or sometimes a bit more complete or analytical, depending on context.

In many situations, both work:

• Eu entendo a questão.
• Eu compreendo a questão.

But entender is usually the more basic and common verb in daily speech.

Yes. Like to understand in English, entender can have a few related uses depending on context.

It can mean:

• to understand
• to know about something
• to interpret something in a certain way
• in some contexts, to be skilled or knowledgeable about something

For example:

• Eu entendo de música. = I know about music.

But in Eu entendo a questão, the meaning is the straightforward I understand the issue/question.

To make it negative, put não before the verb:

• Eu não entendo a questão. = I do not understand the issue.

To turn it into a question, in speech you usually keep the same word order and use intonation:

• Eu entendo a questão? = Do I understand the issue?
• Você entende a questão? = Do you understand the issue?

In writing, the question mark shows it clearly. Portuguese does not usually need an extra helping verb like do in English.

Not always, but very often.

Compare:

• Eu entendo a questão. = I understand the issue/question.
• Isso é questão de tempo. = That is a matter of time.

When you are referring to a specific question or issue, the article is very common:

• a questão
• essa questão
• uma questão

When speaking more generally or in fixed expressions, the article may be absent. So whether you use it depends on the structure and the meaning.