جَاءَنِي زَيْدٌ
Translation: Zayd came to me.
جَاءَ: past-tense verb, built on fatḥ.
نِ: protective nūn; no separate syntactic case position.
ي: attached first-person pronoun, in the accusative position as the object.
زَيْدٌ: nominative subject with visible ḍamma and tanwīn.
Zayd is nominative because it is the subject; the protective nūn does not govern Zayd's case.