In the presence of ladies, you must remove your hat.
Literal
Ladies [subject-が] exist place [at-で] [topic-は] hat [object-を] must-remove.
婦人のいる所では is a relative clause: 'places where ladies are present.' 帽子をとる = 'to remove one's hat.' An old-fashioned etiquette rule from Western culture, expressed in Japanese.