How does one respond to someone who claims that Allah Almighty cannot be seen, reasoning that sight is a characteristic of the weak and created beings, and that Allah knows through more sophisticated means?

If your friend believes in Allah, the Quran, and the Prophet, then you both agree that Allah Almighty cannot be seen, and that knowledge of His attributes comes from His revelation in the Quran or through His Messenger. Allah has described Himself with the attributes of seeing and vision, which are real, intrinsic attributes of His Being, and not merely knowledge. These attributes differ from those of creation, for "there is nothing like unto Him, and He is the All-Hearing, the All-Seeing." So, we affirm for Allah what He has affirmed for Himself, without resemblance or anthropomorphism, and we understand their meanings in a manner befitting His Majesty, for His attributes are perfect and untainted by any deficiency.