It seemed to me as if nothing would or could ever be known. all that had so long engaged my attention suddenly grew despicable.
what change has the character experienced? he no longer enjoys his work.
he has gained a new appreciation for his work.
he has become closer with this friends.
he has taught something to his friends.

 He no longer enjoys his work.

In this excerpt, the speaker tells us that everything that he had previously been interested in suddenly became horrible to him. It is likely that the work the speaker was engaging in stopped being interesting or enjoyable for him. Moreover, he states that he began to feel as if nothing would or could ever be known. Therefore, it seems that the source of his frustration is that the speaker wanted to find out the truth of something, but now believes that it cannot be known.

the star of david was known as the jewish star : d

what is the context here? we need to know what story you're talking about : )