According to a N Korean source in China, rumor has it they knew:
Death of Kim Jong-il: NK Embassy in China Notified Before Announcement (Open Radio for North Korea)
http://english.nkradio.org/news/465
I am certain it was known around Pyongyang on Sunday maybe even Saturday, in many circles, that he was dead. I tend to suspect some of the announcers on North Korean state TV had an inkling, just due to their behavior (I have reviewed p.m. news broadcasts of 18 and 17 December. They may have also heard the Chief Announcer Ms. Ri (aka sobbing “Pyongyang Patty” in the all black chima-chogori dress) was coming out of either retirement, convalescence or hiding, for a special announcement on Monday afternoon at Noon. They might have know this during Sunday and partially Saturday perhaps, any person on the ground would have connected the dots that it mean the demise of Kim Jong il. Word travels fast in Pyongyang among the elite cadre, and further, one of the female announcers did have partial black on when she was on camera on Sunday (prior to the announcement). You have to guess this was picked up by assets in the region during the communication from Pyongyang to the DPRK Embassy in China. Now the question is a) did NSA catch it and process it, and b) was it in the President’s morning briefing for Saturday or Sunday in the USA, i.e. did the US have advance word. Japan is acting as if they were shocked and did not know the way Noda cancelled a stump speech Monday afternoon at Shimbashi JR Train Station in Tokyo and rushed back to the Prime Minister’s office. I am certain if the DPRK Embassy in Beijing got word, Chinese intelligence necessarily intercepted it as well, and/or saw diplomatic personnel movement, such as mass booking of air tickets out, and the like.