He owes me 50 yuan.
Jack is seeing a doctor. JACK是病人/ Jack is seeing a patient.JACK是医生
以下供参考：
(医生治病) see a patient；treat；attend；give medical advice
这位老医生看病很仔细.
The old doctor handles his cases with great care.
(病人就医) see a doctor；consult a doctor；go to a doctor
今天下午我去 看病.
I'm going to see a doctor this afternoon.