Learn Finnish: Tämä on yritys, jonka johtaja on englantilainen. - This is a company whose manager is English.

Jonka is the genitive (possessive) form of the relative pronoun joka. Because we are talking about the manager of the company, we need the genitive form to show possession. In English, this translates perfectly to "whose".

If jonka means "whose", why doesn't johtaja have a possessive suffix like -nsa?

When using the relative pronoun jonka (whose / of which), you just use the regular base form of the following noun. You only need to add possessive suffixes when using personal pronouns like hänen (his/hers) or heidän (theirs).

Why is there a comma before jonka?

Finnish punctuation rules are very strict about this! You must always put a comma before a relative clause (a phrase starting with words like joka or jonka). While English sometimes leaves this comma out, Finnish requires it every time.

Why is englantilainen written with a lowercase letter?

Unlike English, Finnish does not capitalize nationalities, languages, or days of the week. Therefore, words like englantilainen (English person) and englanti (English language) always start with a lowercase letter.