جَاءَنِي الْمَضْرُوبُ غُلَامُهُ.
Translation: The person whose servant was beaten came to me.
جَاءَنِي: main verb and attached object pronoun.
الْمَضْرُوبُ: the overall relative construction is nominative subject; «مَضْرُوب» is a passive participle.
غُلَامُهُ: «غُلَامُ» is the nominative deputy subject governed by the passive participle; «هُ» is a possessive ʿāʾid.
Unlike accusative «زَيْدًا» after the active participle, «غُلَامُهُ» is nominative here because the passive form takes a deputy subject.