Learn Hardcore Finnish: Hän lukee kirjaa ulkona.

In Finnish, when talking about an ongoing or incomplete action (like reading a book but not necessarily finishing it), you typically use the partitive case (kirjaa). The nominative (kirja) or genitive (kirjan) forms would imply a different aspect, such as reading the entire book or talking about the book as a whole entity.

Why is lukee used instead of saying something like "on lukemassa"?

Finnish doesn’t always distinguish between simple present and present continuous as English does. The verb lukee (the 3rd person singular of lukea) can mean both "reads" and "is reading." If you really want to emphasize the ongoing nature of the action, you can indeed say on lukemassa, but it’s not strictly necessary in normal usage.

How does Finnish handle the pronoun hän in terms of gender?

The pronoun hän is gender-neutral in Finnish. It can refer to either a man or a woman (or any other gender). Context usually makes it clear who is being talked about, but grammatically there is no separate feminine or masculine pronoun.

What does ulkona specifically mean, and is there a difference from saying "ulos"?

Ulkona translates roughly to "outside," indicating a location. It answers the question "where?" — "She/He is reading the book outside." Meanwhile, ulos means "(to) outside" and is used when talking about movement or going out (it answers the question "where to?"). So if you want to say someone is moving from inside to outside, you’d use ulos. But if someone is already outside, ulkona is correct.