。
My father works in foreign trade.
Literal
I [of-の] father [topic-は] overseas trade [of-の] work [object-を] doing-is.
仕事をしている ('is doing work [in field X]') is the standard way to say 'works in [field].' 父 is the humble form for one's own father. 海外貿易 is a compound — 海外 ('overseas') + 貿易 ('trade'). Straightforward N4/N3-level description of a family member's profession.