"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)
By now I can answer myself: If a verb is transitive is not determined by the actual use but a principal property of the verb. So if it can in principle be used with a direct object, then it is transitive and needs the transitive form of the past tense.
Thank you Thorsten :-)
For yes/no questions, place the क्या right at the beginning. Basically, you can make a statement into a yes/no question by prefixing with a क्या. For example, the statement तुम सेब खा रहे हो (You are eating an apple) turns into क्या तुम सेब खा रहे हो? (Are you eating an apple?).
When क्या means 'what' in questions, place it just before a verb. For example तुम क्या खा रहे हो? (What are you eating?).
Note: When the sentence has the negation नहीं that needs to go just before the verb, place the क्या before that. Eg: तुम क्या नहीं खाते? (What don't you eat?)