El periodista escribe un reportaje interesante sobre el cambio climático.

Yes. Periodista is a noun that can be masculine or feminine, depending on the person.

• el periodista = the male journalist
• la periodista = the female journalist

The ending -ista does not change here; the article shows the gender.

Escribir is the infinitive, meaning to write. In this sentence, the verb is conjugated to match el periodista:

• yo escribo = I write
• tú escribes = you write
• él / ella escribe = he / she writes

Since el periodista is he or the journalist, Spanish uses escribe.

It can mean both, depending on context.

In Spanish, the simple present often covers:

• he writes
• he is writing

So El periodista escribe... could mean either The journalist writes... or The journalist is writing..., depending on the situation.

Un is the indefinite article, meaning a or an.

• un reportaje = a report
• el reportaje = the report

Here, it introduces a report in a general way, not a specific one already known to the listener.

Not exactly. Reportaje usually means a report, feature report, or news report, often something more in-depth than a simple article.

Depending on context:

• reportaje = report / feature / piece of journalism
• artículo = article
• noticia = news item / news story

So reportaje suggests a journalistic piece, often with more detail.

In Spanish, adjectives usually come after the noun.

So:

• un reportaje interesante = an interesting report

That is the normal word order. English usually puts adjectives before the noun, but Spanish often places them after.

Because interesante is an adjective ending in -e, so it usually has the same form for masculine and feminine singular.

• un reportaje interesante
• una noticia interesante

It only changes in the plural:

• reportajes interesantes
• noticias interesantes

Sobre is a very common way to say about, on, or regarding, especially with topics.

So:

• sobre el cambio climático = about climate change

Other options exist, such as acerca de, but sobre is very natural here.

Spanish often uses the definite article more than English does.

Here, el cambio climático refers to the concept climate change as a known, specific phenomenon. In Spanish, that normally takes the article:

• el cambio climático
• la historia
• la política

English sometimes drops the in these cases, but Spanish often keeps it.

The accent mark shows where the stress goes: cli-MÁ-ti-co.

Without the accent, Spanish pronunciation rules would suggest a different stress pattern. The written accent helps show the correct pronunciation and spelling.

Usually, you can leave out the subject pronoun in Spanish, but here el periodista is not a pronoun; it is the full noun phrase the journalist.

You could say just Escribe un reportaje interesante... if the subject is already clear from context, but then it would mean something like:

• He/She is writing an interesting report...

Keeping El periodista makes it clear exactly who is doing the action.

Yes, it is possible, but it is less neutral.

• un reportaje interesante = the normal, standard way
• un interesante reportaje = more literary or stylistically marked

Putting the adjective before the noun can add emphasis or a slightly more formal tone. For everyday Spanish, un reportaje interesante is the safer choice.