잘 오나 봐 means "I guess he/she comes here often" 잘 오나 봐? means "I guess he/she comes here often, doesn't he/she?" 잘 오(다) + 나 보(다) + 아(ending suffix) 잘 오다 to come often/well https://sydneytoseoul.wordpress.com/2012/02/11/a%EC%9C%BC%E3%84%B4%EA%B0%80-%EB%B3%B4%EB%8B%A4-v%EB%82%98-%EB%B3%B4%EB%8B%A4-it-seems/ A+(으)ㄴ가 보다, V+나 보다 ~ It seems… This expression can be used to express ones speculation, or you are inferring something occurred. Structure 1) Present tense a] V+나 보다 b] A+(으)ㄴ가 보다 c] N+(이)ㄴ가 보다 2) Past tense a] V/A+았/었나 보다 b] N+이었/였나 보다 Examples 엄마는 전화 안 해서 바쁜가 봐요. Since Mum didn’t call I guess she is busy. 서현씨는 피곤하나 봐요. 어제 밤에 못 잤나 봐요. Seohyun seems tired. She mustn’t have sleep last night. 사람이 많았나 봐요. I guess there was a lot of people.