jemandes mutter hat 4 söhne nord süd ost wie heißt der vierte sohn

The fourth son’s name is Wie. In the riddle, the setup lists Nord, West, and Süd, and the question asks for the name of the fourth son, which is revealed by the wording of the sentence itself: “Jemandes Mutter hat vier Söhne. Nord, West und Süd.” The implied name is the word that appears as the fourth item in the sequence: Wie.