migrate oracle TH8TISASCII to postgres equivalnt win874

Hey Guys ,

im trying migrate DB from oracle charset TH8TISASCII to postgres closed equivalent WIN874 , but seems few chars are not transferred successfully  .

1. do you know which characters are not fully covered in win874 when converting from TH8TISASCII. 

2. how do i fetch it in the oracle level before doing the migrate ? 

thx .