جَاءَ غُلَامِي — My servant came.
جَاءَ is a past-tense verb.
غُلَامِي is its nominative subject; ḍammah is estimated because the final consonant bears a kasrah suited to the possessive yāʾ. The stem is the mudāf.
-ي is the attached possessive pronoun as mudāf ilayh (genitive position).
The nominative analysis is determined by its function as subject.