Typically for communications in English / Korean Americans they’ll write family names at end.

Common family names (tend to be much more concentrated than Prevalence in most other countries): Park (or Bak, Pak), Lee (or Ree, Rhee, Yi), Kim, Cho (or Jo), Kang (or Gang), Jeong (Cheong, Chung, Jung), Choi (Choe), Yun (Yoon), Im, Rim, Chang (Jang), Hwang, Song, etc.

Chinese method is similar. But there are a few common two-syllable family names (like Ouyang) and it’s more common to have a one syllable personal name but still overwhelmingly common to have two syllable.

If you ever have to guess, guess that the two-syllable one is the personal name.