Learn Hardcore French: Paul pense à sa carrière d'ingénieur quand il choisit une nouvelle formation. - Paul thinks about his engineering career when he chooses a new training course.

penser à + noun/pronoun = to think about, to have in mind
- Paul pense à sa carrière. → Paul is thinking about his career.
penser de + noun = to think of, to have an opinion about
- Que penses-tu de sa carrière ? → What do you think of his career?
penser sur is almost never used in everyday French. If you translate English “think about something” directly as penser sur, it will sound wrong.

In your sentence, Paul is simply thinking about his career while choosing training, so penser à is the natural choice.

Does sa mean “his” or “her” here? Why is it sa carrière and not son carrière?

sa, son, ses agree with the gender and number of the noun, not with the person who owns it.
carrière is feminine singular → you must use sa.

So:

sa carrière = his career / her career (feminine noun, singular)
son métier = his job / her job (masculine noun, singular)
ses études = his studies / her studies (plural)

In context, we know Paul is male, so sa carrière is understood as his career, but grammatically it’s feminine because carrière is feminine.

Why is it sa carrière d’ingénieur and not sa carrière comme ingénieur? Are both possible?

Both are possible, but there is a nuance:

sa carrière d’ingénieur is the most common way to say “his career as an engineer”.
- Pattern: carrière de + profession (which becomes d’ before a vowel).
- It sounds neutral and idiomatic.
sa carrière comme ingénieur also exists, but:
- comme + profession often emphasizes the role or function.
- It can sound a bit more descriptive or contrastive: “in his capacity as an engineer, as opposed to something else.”

In normal speech, sa carrière d’ingénieur is the standard, natural choice.

Why is it d’ingénieur and not de ingénieur or d’un ingénieur?

Three points:

Elision (de → d’)
- de becomes d’ before a vowel or silent h:
  - de ingénieur → d’ingénieur
- This is just a pronunciation/spelling rule.
No article before the profession
After words like carrière de, métier de, travail de, French normally omits the article before a profession:
- une carrière d’ingénieur, son métier de professeur, etc.
  Saying d’un ingénieur here would suggest “a career of an engineer,” which sounds odd.
Meaning
- carrière d’ingénieur = a career as an engineer (general, not “of a particular engineer”).

What exactly does formation mean? Is it like “education” or “training”?

Formation is a tricky false friend:

It usually means training, course, program, or professional education, often specific and practical:
- une formation en informatique = an IT training / a computer course
- une formation continue = continuing/professional training
It is not normally used for general “education” in the broad sense:
- “He had a good education” → Il a reçu une bonne éducation, not formation.

In your sentence, une nouvelle formation is best understood as “a new training course/program”, not “a new (whole) education”.

Why is it une nouvelle formation and not la nouvelle formation?

une nouvelle formation = a new training course (non-specific; one among others)
la nouvelle formation = the new training course (a specific one already known in the context)

Because the sentence doesn’t point to a particular, already-identified course, French uses the indefinite article une. It just means he’s choosing one new training program, not “the” specific one you and I already know about.

Why is the adjective nouvelle placed before formation? Could we say formation nouvelle?

In French, many common adjectives can go before or after the noun, but the position usually changes the nuance.

une nouvelle formation (normal choice here)
- Focus: new in the sense of additional, recent, different from the previous one.
- This is the standard way to say “a new training course”.
une formation nouvelle
- More literary or stylistic.
- Focuses on the novel, innovative character of the training itself (unusual, original).

In everyday speech, une nouvelle formation is what you would say.

Both verbs are in the present: pense and choisit. Is this talking about now, or about something that happens regularly?

In French, the present tense can express several ideas:

Action happening right now
- It could mean: Right now, as he is choosing a new training, he is thinking about his career.
Habit / general truth (very common with quand)
- More likely here: Whenever he chooses a new training course, he thinks about his career as an engineer.

Context would decide which reading is intended, but quand + present / present is a typical pattern for repeated or general situations.

Could we say Quand il choisit une nouvelle formation, Paul pense à sa carrière d’ingénieur instead?

Yes, that’s completely correct.

Paul pense à sa carrière d’ingénieur quand il choisit une nouvelle formation.
Quand il choisit une nouvelle formation, Paul pense à sa carrière d’ingénieur.

Both mean the same thing.
When you start the sentence with Quand, you normally add a comma after the quand-clause. The choice is mostly about emphasis and style:

Starting with Paul: focus first on Paul and what he does.
Starting with Quand il choisit…: focus first on the circumstance.

Could we replace quand with lorsque here? Is there any difference?

Yes, you can say:

Paul pense à sa carrière d’ingénieur lorsqu’il choisit une nouvelle formation.

Differences:

quand = “when”; very common, neutral, used everywhere.
lorsque = also “when”; a bit more formal or written, slightly more elegant.

In everyday spoken French, quand is more frequent. In written or more formal language, lorsque is also very common. The meaning here is practically the same.

Could we drop il and say “quand choisit une nouvelle formation” like in some other languages?

No. In French, you must keep the subject pronoun:

Correct: quand il choisit une nouvelle formation
Incorrect: quand choisit une nouvelle formation

Unlike Spanish or Italian, French is not a “pro-drop” language: subject pronouns (je, tu, il, elle, nous, vous, ils, elles) are almost always required.

Is there a difference between choisir quelque chose and choisir de faire quelque chose?

Yes:

choisir quelque chose = to choose something (direct object)
- Il choisit une nouvelle formation. → He chooses a new training course.
choisir de + infinitive = to choose to do something
- Il choisit de suivre une nouvelle formation. → He chooses to take a new training course.

In your sentence, choisit une nouvelle formation correctly uses choisir + direct object.