"What have you written?"
Translation:तुमने क्या लिखा है?
Exactly! तुमने किताब लिखी है = You have written a book. (Since किताब is feminine.) However this rule only works in the ने form of past tense. With nontransitive verbs, the verb agrees with the subject, "You went home" translates as तुम घर गई (Said to a female), तुम घर गए (Said to a male)