Learn Finnish: Onko sinulla veli? - Do you have a brother?

Finnish doesn't actually have a verb that means "to have"! Instead, it uses a special structure that literally translates to "at someone is something." Here, sinulla means "at you" or "on you", and on means "is". So, literally, this sentence asks "Is there a brother at you?"

Why does the verb on have -ko at the end?

The -ko suffix is a question particle. When you add it to a word and put that word at the beginning of the sentence, it turns a statement into a yes/no question. The basic statement is Sinulla on veli (You have a brother). Adding -ko to the verb on and moving it to the front gives us Onko sinulla veli? (Do you have a brother?).

Could I ask this by saying Sinulla onko veli?

No, in Finnish yes/no questions, the word with the -ko or -kö attached to it must always be the very first word in the sentence.

Why is veli in its basic dictionary form? Shouldn't it be an object?

In English, "a brother" is the object of the verb "have". But in the Finnish "to have" structure ("at you is a brother"), veli is grammatically the subject of the sentence. Because it acts as the subject, it stays in its basic dictionary form, which is called the nominative case.