Learn French: Voici la femme dont le mari est très jaloux. - Here is the woman whose husband is very jealous.

In English, we drop the article after "whose". But in French, when using dont for possession, you must keep the definite article (le, la, l', or les) in front of the noun being possessed. Think of it literally as "of whom the husband".

I learned before that dont means "of which" or "about whom". Why does it mean "whose" here?

The pronoun dont replaces any phrase that starts with the preposition de (of). If we made this two separate sentences, they would be: Voici la femme. (Here is the woman) and Le mari de la femme est très jaloux. (The husband of the woman is very jealous). By replacing de la femme, dont perfectly translates to the English "whose".

Since the sentence is about la femme, why does the adjective jaloux take a masculine form instead of being feminine?

The adjective must always agree with the noun it actually describes. Even though the relative pronoun dont links back to the woman, the person who is actually jealous is the husband (le mari). Because mari is masculine singular, we use the masculine form jaloux instead of the feminine jalouse.

Could I use qui or instead of in this sentence?