I just came across this phrase for the first time in 1984, book 2 chapter 4. The sentence reads (speaking of Mr. Charrington):
Nor did he seem shocked or become offensively knowing when it was made clear that Winston wanted the room for the purpose of a love-affair.
It also appears in Newton Booth Tarkington's Gentle Julia:
He wore a fully developed moustache, an easy smile, clothes offensively knowing; and his hair began to show that scarcity which Julia felt gave him distinction—a curious theory, but natural to her age.
I've never encountered this phrase before and can't find a definition online, though it is itself used in Wordsmyth's definition of "smirk".
Does anyone have a clear definition of the phrase?