Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
According to Kinbote (in VN’s novel Pale Fire, 1962, Shade’s mad commentator who imagines that he is Charles the Beloved, the last self-exiled king of Zembla), on his deathbed Conmal (the Zemblan translator of Shakespeare) called his nephew, Charles Xavier Vseslav (aka Charles the Beloved), "Karlik:"
According to Van Veen (the narrator and main character in VN’s novel Ada, 1969), oblivion is a one-night performance:
Describing the picnic on Ada’s sixteenth birthday, Van Veen (the narrator and main character in VN’s novel Ada, 1969) mentions a little camel of yellow ivory carved in Kiev, five centuries ago, in the days of Timur and Nabok:
Describing his reunion with Ada in 1922, soon after her husband’s death, Van Veen (the narrator and main character in VN’s novel Ada) mentions Swiss-German Louis Wicht who now managed Les Trois Cygnes (Van’s hotel in Mont Roux) instead of his late father-in-law Luigi Fantini:
Describing his childhood travels, Van Veen (the narrator and main character in VN’s novel Ada, 1969) mentions Goethe's and d'Annunzio's marble footprints reverently pointed out to him by AAA (Andrey Andreevich Aksakov, Van’s Russian tutor):
Before the family dinner in “Ardis the Second” Van Veen (the narrator and main character in VN’s novel Ada, 1969) tells Demon Veen (Van’s and Ada’s father) that the Ardis tap water is not recommended:
According to Van Veen (the narrator and main character in VN’s novel Ada, 1969), his tutor Andrey Andreevich Aksakov (AAA) blew his fat red nose, when shown the peasant-bare footprint of Tolstoy preserved in the clay of a motor court in Utah:
Describing his life with Cordula de Prey in Cordula’s Manhattan flat, Van Veen (the narrator and main character in VN’s novel Ada, 1969) compares his work on his first novel Letters from Terra to pregnancy and childbearing:
Trying to remember his family name, Vadim Vadimovich (the narrator and main character in VN’s novel Look at the Harlequins!, 1974) wonders if his surname is Nebesnyy:
Before the family dinner in “Ardis the Second” Ada (the title character of a novel, 1969, by VN) mentions a delicate little birthwort (the unfortunate plant that, according to Van, used to be considered by the ancient inhabitants of the Ladore region not so much as a remedy for the bite of a reptile, as the token of a very young woman’s easy delivery):