«الَّذِي حَضَرَ مُجْتَهِدٌ»: «الَّذِي» is a nominative mubtadaʾ; «حَضَرَ» is the ṣilah with implicit subject as ʿāʾid; «مُجْتَهِدٌ» is the predicate.
«أَكْرَمْتُ الَّذِي حَضَرَ»: «الَّذِي» is an accusative object, while the same ṣilah and ʿāʾid remain.
External syntax determines the relative noun’s case position; internal syntax determines the structure of its ṣilah.