In an emergency, can an airliner land at Pyongyang or another North Korean airport?
I can see at least three questions here and only one of them is fully aviation-related. First, can an airliner legally divert to Pyongyang in an emergency, under the laws of its own country? For US airlines, the answer is yes. 14 CFR 91 SFAR 79 bans flights over North Korea, but does allow an exception in an emergency:


  2. Flight Prohibition. Except as provided in paragraphs 3 and 4 of this SFAR, no person described in paragraph 1 may conduct flight
  operations through the Pyongyang FIR west of 132 degrees east
  longitude.
  
  [...]
  
  4. Emergency situations. In an emergency that requires immediate decision and action for the safety of the flight, the pilot in command
  on an aircraft may deviate from this SFAR to the extent required by
  that emergency.


Second, will North Korea allow the airliner to land? This is a political question, not an aviation one. Either they say yes or they say no. If they say no to an airliner in distress, how will they enforce that? Are they willing to shoot it down rather than let it land? Would that decision depend on the country of the airliner? Can they even make that decision within minutes, or is it already made and they simply initiate a defined procedure? The pilot is probably just going to try to land anyway; assuming the alternative is a crash, he would have little to lose.

Finally, what will the 'reception committee' on the ground look like? No idea, this is a political/military question.

But practically speaking, this situation should never arise anyway (ignoring movie plot stuff like hacked navigation systems). If your country isn't friendly or at least neutral to North Korea, your airlines simply won't plan flights where the only emergency landing possible is in Pyongyang, and for US carriers specifically it would be illegal anyway.