In "Alexandr Pushkin: Eugene Onegin, A Novel in Verse. Translated by Vladimir Nabokov," vol. II, Princeton, Bollingen, pages 176-178, we find in an entry about granite a detailed commentary that begins with: "In the stanza Onegin and Pushkin are on the south bank of the Neva, on the stretch called the Palace Quay, and stand facing the Petropavloskaya Krepost', the SS. Peter and Paul Citadel, a fortress used as a prison for political offenders..."
Nabokov located Pushkin's sketch in a Leningrad 1937 edition (ed.A. Slonimski and E.Gollerbach) and explains the entire setting, Pushkin's intentions when he suggested this illustration to his publisher and the resulting unfortunate sketches by Aleksandr Notbek.

Here, after crossing Bridge Kokushkin,
With bottom on the granite propped,
Stands Aleksandr Sergeich Pushkin;
Near M'sieur Onegin he has stopped.

Ignoring with a look superior
The fateful Power's citadel,
On it he turns a proud posterior:
My dear chap, poison not the well!”

Brian Boyd, in Vladimir Nabokov The American Years describes this episode from a different perspective: "..the 'miserably bad' engraver Alexander Notbek (Nabokov does not exaggerate) whose 1829 illustrations of Eugene Onegin inspired Pushkin to two acid epigrams. Asked by Bollingen Press to delete references to a more recent artist's 'hideous and absurd illustrations' Nabokov responded that his criticism was 'so dear to me that I would prefer giving up the publication of my entire work rather than surrendering that passage.' An overstatement, no doubt, but the decay of the unique contribution of genius as it becomes corrupted by 'average reality' was too central a theme of his whole enterprise for him to withdraw and attack." (p349/350.).

What originally prompted my search was related to "editorial censorship" but, inspite of all the findings reproduced above, I couldn't find out from what edition the word "bottom" was deleted or substituted by a dash. Boris Schnaiderman ("Tradução, Ato Desmesurado", Ed. Perspectiva, 2011) mentions a prudish editorial censorship to this particular epigraph with a mention of Pushkin's bottom (the "offensive" word!) leaning against a granite ledge.

*"In 1829, Alexander Pushkin mentioned Kokushkin bridge in a famous epigram. For the first edition of Eugene Onegin, the poet commissioned an illustration depicting himself and Onegin walking together along the quay. Upon receiving the illustration, which represented him leaning on a parapet with his back turned towards the Peter and Paul Fortress, he was exceedingly displeased with the result (which had little in common with his own preliminary sketch, illustrated to the right) and scribbled [this] epigram Fyodor Dostoevsky's Crime and Punishment starts with a mention of the bridge: “On an exceptionally hot evening early in July a young man came out of the garret in which he lodged in S. Place and walked slowly, as though in hesitation, towards K. bridge" (wikipedia)

** In his novel Eugene Onegin, Alexander Pushkin depicted himself walking along Palace Quay with his hero, Eugene Onegin:
Filled with his heart's regrets, and leaning
Against the rampart's granite shelf,
Eugene stood lost in pensive dreaming
(As once some poet drew himself).
The night grew still... with silence falling;
Only the sound of sentries calling,
Or suddenly from Million Street
Some distant droshky's rumbling beat;
Or floating on a drowsy river,
A lonely boat would sail along,
While far away some rousing song
Or plaintive horn would make us shiver.
But sweeter still, amid such nights,
Are Tasso's octaves' soaring flights.
For the first edition of this chapter, the poet commissioned an illustration depicting him and Onegin walking together along the quay. Upon receiving the illustration, which represented him leaning on a parapet with his back turned towards the Peter and Paul Fortress, he was exceedingly displeased with the result (which had little in common with his own preliminary sketch, illustrated to the right) and scribbled the ...epigram underneath: