أَسُكَّانَ نُعْمَانِ الْأَرَاكِ تَيَقَّنُوا
O dwellers of Nuʿmān al-Arāk, be certain.
A is the vocative particle; sukkāna is an accusative vocative in an iḍāfah construction, with Nuʿmāni as a genitive complement. Tayaqqanū is an imperative addressed to a plural audience.
فِي رُبْعِ قَلْبِي سُكَّانُ
They dwell in a quarter of my heart.
The speaker does not intend literal habitation. The phrase vividly expresses a cherished place within his feelings. Syntax and imagery reinforce the rhetorical call.