He pretends not to know about it
不等于
He doesn't pretend to know about it
他不是假装知道这件事
he doesn't/didn't pretend to know
他不是假装不知道
he doesn't/didn't pretend not to know(not to have known)
He pretends not to know about it
不等于
He doesn't pretend to know about it
他不是假装知道这件事
he doesn't/didn't pretend to know
他不是假装不知道
he doesn't/didn't pretend not to know(not to have known)