What is the most notable hypostyle of mosque?
Please refer this link for answers
"Most notable" is probably a matter of opinion, but according to the site you reference, the Mezquita mosque in Cordoba, Spain stands out as particularly unique or noteworthy. Hypostyle, or Arab-plan mosques tend to have a rectangular construction with an enclosed courtyard, and tend to rely on columns for structural support while still providing shade for visitors. The Mosque in Cordoba has over 850 columns, and the author of the article you reference believed that particular example of hypostyle to be exceptionally noteworthy.