Learn Finnish: Miksi opiskelija palaa kotiin? - Why does the student return home?

The verb palata (to return) is a movement verb. In Finnish, verbs that express movement towards a destination require a directional case, like the illative ('into') case. You must use kotiin (to home), whereas kotona (at home) is a static case used with non-moving verbs like olla (to be).

Why does the verb palaa look so different from its dictionary form?

The dictionary form is palata (to return), which is a Type 4 verb (verbs ending in -ta or -tä). To conjugate it, you drop the -ta to get the stem palaa-. The third-person singular (he/she/it) usually doubles the last vowel of the stem, but since there are already two 'a's, it simply stays palaa.

Why isn't there a -ko or -kö ending in this sentence to make it a question?

The word miksi (why) is already a question word. You only attach the -ko or -kö suffix to a verb or a noun when you are asking a yes/no question. Since this is a 'why' question, the question word does all the work.

Does the word opiskelija come from the verb for studying?

Yes! It comes from the verb opiskella (to study). The -ja or -jä suffix in Finnish is often used to turn a verb into a noun for the person doing that action, very much like the '-er' ending in English (such as bake becoming baker).