Learn Hardcore French: C’est le livre dont je te parle. - This is the book I am talking to you about.

Dont is a relative pronoun that replaces de + [noun]. The base sentence is Je te parle de ce livre. When you turn de ce livre into a relative clause, it becomes le livre dont je te parle (“the book [about which] I’m talking to you”).

Why not que or qui?

Que replaces a direct object and qui replaces a subject. Here, the noun is the complement of de after parler de, so you need dont, not que/qui. Saying … que je te parle or … qui je te parle is incorrect.

Can I say C’est le livre que I’m talking to you about in French, i.e., C’est le livre que je te parle de?

No. French doesn’t “strand” the preposition at the end. Use one of:

C’est le livre dont je te parle.
Je te parle de ce livre.
C’est de ce livre que je te parle.

Could I use duquel instead of dont?

You could say C’est le livre duquel je te parle, but it sounds stiff. Prefer dont after verbs/adjectives that take de. Forms of lequel (e.g., duquel, de laquelle) are mostly used when de is part of a longer preposition (e.g., près de, loin de): la ville près de laquelle j’habite.

What does te mean here?

Te is the indirect object pronoun “to you” (familiar singular), because parler is used as parler à quelqu’un (“to speak to someone”). So je te parle = “I’m speaking to you.”

Can I use toi instead of te?

Not in this position. Toi is the stressed form used after prepositions or for emphasis: à toi. For example, C’est à toi que je parle (“It’s you I’m talking to”). Without a preposition, use te.

Where do pronouns go with parler in negatives and past tenses?

They go before the conjugated verb:

Affirmative: Je te parle de ce livre.
Negative: Je ne te parle pas de ce livre.
Passé composé: Je t’ai parlé de ce livre. (elision: te → t’ before a vowel)

Can I also use en here?

Use either dont or en, not both for the same thing. If the book isn’t named, say Je t’en parle (“I’m talking to you about it”). If you name it in a relative clause, say C’est le livre dont je te parle. Don’t say dont je t’en parle.

Why C’est and not Il est?

Use C’est to identify/point to something before a noun with a determiner: C’est le livre…. Il est doesn’t take a noun with an article in this way; it’s used with adjectives or professions: Il est intéressant; Il est professeur.

Why the definite article le? Could I use un or ce?

Le points to a specific, known book (“the one we’ve been talking about”). Un would mean “a/one book I’m telling you about” (non-specific). Ce is possible for emphasis or deictic pointing: C’est ce livre dont je te parle (“It’s this very book I’m telling you about”).

How do I say it in other tenses?

Past (passé composé): C’est le livre dont je t’ai parlé.
Imperfect: C’est le livre dont je te parlais.
Future: C’est le livre dont je te parlerai.
Conditional: C’est le livre dont je te parlerais (si …).

Does dont change form or agree with anything?

No. Dont is invariable—no gender or number changes.

Which verbs/adjectives commonly require dont?

Many that take de:

Verbs: parler de, se souvenir de, rêver de, discuter de, se servir de, se méfier de, s’occuper de, manquer de, avoir besoin de, avoir envie de.
Adjectives: fier de, content de, capable de, responsable de, jaloux de. Example: C’est la personne dont je me souviens.

Is a comma needed before dont here?

No. This is a restrictive relative clause (it identifies which book), so no comma. Commas appear with non-restrictive clauses: Ce livre, dont je te parle depuis des semaines, est épuisé.

How do I pronounce the sentence?

Approximate: “seh luh leevr dôn zh tə parl.” Tips:

dont = nasal vowel [dɔ̃]; the final t is silent (no liaison: dont je = [dɔ̃ ʒə]).
je te often reduces to [ʒtə] in running speech.

Can I front the de-phrase for emphasis?

Yes: C’est de ce livre que je te parle. This cleft construction emphasizes de ce livre (“it’s this book that I’m talking to you about”).

How does it work with plural or feminine nouns?

Feminine: C’est la revue dont je te parle.
Plural: Ce sont les livres dont je te parle. Dont doesn’t change.

Could I use auquel here?

No. Auquel corresponds to à + lequel and is used with verbs that take à (e.g., penser à → auquel je pense). Here the relation is de (because parler de [thing]), so you need dont.

Can I use sur with parler to mean “about”?

No. Use parler de (“talk about”). Sur can mean “about” in other contexts (e.g., un livre sur les volcans = “a book about volcanoes”), but with parler, the idiomatic preposition is de.

I learned dont can mean “whose.” Does it mean that here?

Here it means “of/about which.” But yes, dont can also mark possession: la femme dont le fils est médecin (“the woman whose son is a doctor”).