عَلَى: preposition.
كَمْ: declarative kam, indeclinable but in a genitive position after ʿalā.
رَجُلٍ: genitive declarative tamyīz.
حَكَمْتَ: past verb and second-person subject.
The source illustrates the declarative reading here; a genuinely interrogative reading would use an accusative singular tamyīz in the basic pattern.