Hallo
Andreas,
Jostein is an Old Norse name:
jór = horse
steinn = stone
The pronunciation is: YOU-stayn (die deutsche Beschreibung der Aussprache wäre ungefähr: JUU-ßtäin). The stress is on the first syllable.
In Iceland the name is written Jósteinn.
Viele Grüße
Satu