Eu ainda tenho uma dúvida sobre a última lição.

Yes, you can often leave eu out in Portuguese.

Portuguese is a pro-drop language, which means the verb form often already tells you who the subject is. In tenho, the ending shows I have, so Tenho uma dúvida... is perfectly natural.

Including eu adds a little more emphasis or clarity, for example:

• Eu ainda tenho uma dúvida... = I still have a question/doubt...
• Ainda tenho uma dúvida... = same basic meaning, but slightly less explicit/emphatic

So both are correct.

Here, ainda means still.

So:

• Eu ainda tenho... = I still have...

It shows that the doubt/question remains unresolved.

Depending on context, ainda can also mean yet or even even, but in this sentence still is the best match.

In Portuguese, the usual expression is ter uma dúvida = to have a doubt / to have a question.

So:

• Tenho uma dúvida. = I have a question / I have a doubt.

English speakers sometimes expect a structure closer to I am in doubt, but that is not the normal choice here.

Be careful, though:

• Estou em dúvida means I’m unsure / I’m undecided
• Tenho uma dúvida means I have a question / I have one point I don’t understand

They are related, but not identical.

It can mean both, depending on context.

Literally, dúvida is doubt, but in many everyday learning/classroom situations, tenho uma dúvida is commonly used where English would often say:

• I have a question
• I’m confused about something
• There’s something I don’t understand

So in a classroom context, uma dúvida often works very much like a question.

Using uma is the most natural way to express a doubt / a question here.

• Tenho uma dúvida = I have a question
• Tenho dúvida can exist, but it usually sounds more general or less countable, depending on context

In this sentence, uma dúvida suggests one specific unresolved point about the lesson.

Yes, both can work, but they are not exactly the same.

• sobre a última lição = about the last lesson
• da última lição = from the last lesson or about the last lesson, depending on context

In your sentence, sobre clearly marks the topic:

• Tenho uma dúvida sobre a última lição. = I have a question about the last lesson.

If you say:

• Tenho uma dúvida da última lição.

it may sound a bit more like the doubt comes from that lesson. It is understandable, but sobre is the clearer and more standard choice when you mean about/regarding.

Because lição is a feminine noun.

So the article and adjective must agree with it:

• a lição
• a última lição

Agreement in Portuguese is very important:

• lição = feminine singular
• a = feminine singular article
• última = feminine singular adjective

If the noun were masculine, you would use o último instead.

Usually it means the last lesson, often in the sense of the most recent lesson.

So in many contexts:

• a última lição = the last/recent lesson

Depending on context, última can also mean final, but here it will normally be understood as the previous most recent lesson.

Yes, but the meaning changes slightly.

• lição often means lesson, as in the content studied
• aula usually means class, as in the session itself

So:

• Tenho uma dúvida sobre a última lição. = question about the lesson/content
• Tenho uma dúvida sobre a última aula. = question about the last class/session

In many contexts, both are possible, but lição focuses more on the material.

The stress is marked by the written accents:

• dúvida → stress on dú
• última → stress on úl

Approximate pronunciation:

• dúvida ≈ DOO-vee-da
• última ≈ OOL-chee-ma or OOL-ti-ma, depending on accent/region

The accent marks are not optional here; they show the stressed syllable and are part of the correct spelling.

Yes, but it changes the meaning.

• Tenho uma dúvida = I have one question / one doubt
• Tenho dúvidas = I have doubts / I’m uncertain / I have several questions

So the singular uma dúvida is more specific, while the plural dúvidas sounds broader or more general.

The given order is the most natural:

• Eu ainda tenho uma dúvida sobre a última lição.

But some variation is possible:

• Ainda tenho uma dúvida sobre a última lição.
• Eu tenho ainda uma dúvida sobre a última lição. — grammatically possible, but less natural in everyday speech
• Sobre a última lição, eu ainda tenho uma dúvida. — more emphasis on the topic

So the original sentence is a very standard and natural way to say it.