Questions can be formed by adding the suffix -ko/kö after the verb.
The verb is thus inflected as normal, and a suffix is added, and a question mark at the end of the sentence.
-As the answer to the questions is always yes or no.

You can add -ko/kö to any word in a sentence if you want to emphasize that word in particular, but otherwise the suffix is added after the inflected verb.

Add - ko to the end of the word when the word contains the letters a, o or u. (The word may also contain the letters e or i.)
Add - kö to the end of the word when the word contains the letters y, ä or ö.
The word “kö” is added to the end of the word when the word contains the letters e or i, but not the letters a, o, u, y, ä or ö.

(Sinä) puhut englantia. -> Puhutko (sinä) englantia?