In Pniniad: Vladimir Nabokov and Marc Sceftel Galya Diment writes: "Most critics agree... that Pnin probably owes his name to the late eighteenth-century Russian publicist and minor poet Ivan Petrovich Pnin..." and mentions VN's possible source: Vladimir Orlov's "Русские просветители 1790-х-1800-х гг." (Russian Enlighteners, 1790s-1800s) that focuses on several minor men of letters of the post-Radishchev era. But, I suspect, VN also knew "Иван Пнин. Сочинения" (The Works of Ivan Pnin), М., Издательство всесоюзного общества политкаторжан и ссыльно-поселенцев, 1934, Классики революционной мысли домарксистского периода, edited by I. A. Teodorovich, with the introductary biographical essay by I. K. Luppol and commentaries by V. N. Orlov.*

Remembered mainly thanks to Batyushkov's elegy "На смерть И. П. Пнина" (On the Death of Pnin, 1805), I. P. Pnin (1773-1805) is the author of "На смерть Радищева" (On the Death of Radishchev, 1802).** In his EO Commentary (vol. II, p. 312) VN mentions Radishchev and his ode "Вольность" (Liberty):

Some Soviet editions replace, in l. 15 [of Pushkin's Exegi Monumentum], the words v moy zhestokiy vek ("in my cruel age" or "times") by an earlier MS variant: vsled Radishchevu ("in the wake of Radishchev"), an allusion to Alexander Radishchev's ode, Liberty (Vol'nost'; written c. 1783), and to Pushkin's own ode, Vol'nost' (written 1817). In the wake of Pushkin, the author of Pnin "exalted freedom in [his] cruel age and called for mercy toward the downfallen."

The land of liberty and its great statue are mentioned in Pnin (Chapter Two, 5): And at last, when the great statue arose from the morning haze where, ready to be ignited by the sun, pale, spellbound buildings stood like those mysterious rectangles of unequal height that you see in bar graph representations of compared percentages (natural resources, the frequency of mirages in different deserts), Dr Wind resolutely walked up to the Pnins and identified himself--'because all three of us must enter the land of liberty with pure hearts.'

*Teodorovich and Luppol (who shared a prison cell with Vavilov) perished in the Stalin camps, Orlov managed to survive and later wrote a book on Blok (Gamayun. The Life of Alexander Blok, 1977).