Learn Finnish: Mikä on koiran nimi? - What is the dog's name?

We add the letter -n to the end of the word koira (dog) to make it koiran. This is called the genitive case, and it works just like adding an apostrophe and an s ('s) in English to show possession.

Why is the word for "name" placed right after "koiran"?

In Finnish, the possessor (the one who owns something, like koiran) almost always comes directly before the thing being owned (nimi). It perfectly matches the English word order of "the dog's name".

I often see "mitä" used for "what". Why does this sentence use "mikä"?

Both mikä and mitä mean "what". We use mikä when asking to identify a specific, complete thing in its basic form, like a name. Mitä is used for substances, uncountable things, or ongoing actions. Since a name is a specific single thing, we use mikä.