How can one reconcile understanding Allah's attribute of "Sovereignty" (al-Mulk) with His saying: "There is nothing like unto Him, and He is the All-Hearing, the All-Seeing," knowing that the modality is unknown?

One must differentiate between the attributes of Allah and their effects. The 'how' of the attributes themselves is inconceivable, whereas the 'how' of their effects is conceivable through observing them in creation. These effects point to the Creator and His attributes. The Quran is replete with mentions of the observable effects of Allah's attributes, such as the manifestation of the name "The Creator" in creation, and the name "The Sustainer" in the existence of sustenance, and "The Most Merciful" in the diffused mercy, and similarly, every one of Allah's beautiful names has a witness in His creation and command. All existing things are witnesses to Allah's attributes, descriptions, and names, and they point to them through intellect, senses, innate disposition, contemplation, and reflection.