잠자는 자는 is composed of
잠자(다)+는(1) 자+는(2)
잠자(다) means "to sleep"
는(1) is a determiner particle
자 is means "man, person"
는(2) is a topic marker
잠자는 자 means "a person who is sleeping"
권리 위에 잠자는 자는 보호받지 못한다 means
A person who is sleeping on rights cannot be protected.