Hesses parents were missionaires.. Hesses thoughts about other religions, God and universe are very well presented in his books, but I haven't read a word about Jesus.

So, does anybody kow, how did he understand Jesus?

He was unlimited in religiosty.
You can read about his idea of religion in witing Kindheit des Zauberers or in Madonnenfest in Tessin or in other autobiographical writing
You are right . He didnt say a word about Jesus. I think he took same parts from Gospel for his ideas. That's all.