I haven't got my copy of the novel handy,
but if I recall correctly, not long before the phrase "..qu'il t'y
méne.." , HH's narration refers rather mockingly to the genre of
detective literature that drops broad hints to the solution in italics. So then,
of course, shortly thereafter, because the phrase is in French, it appears in
italics ! A wonderful typically Nabokovian joke for the informed reader. The
translation - "that he lead you there" or "that he should lead you there"
(subjunctive tense) - leads my mind to an obvious interpretation: "that the
author lead you (us the readers)" to a finding, in this case, the all-important
solution to the "detective mystery" - who abducted Lolita?