。
Every day I visited my sick friend.
Literal
Every-day I [topic-は] sick [possessive-の] friend [object-を] visited.
訪ねる ('to visit a person') takes を for the person visited. 病気の友人 uses the noun 病気 ('illness') to modify 友人 via の. The explicit 私は is somewhat marked — natural speech would often omit it.