Former intel analyst...

Journalists get into NK with fewer problems than anyone else, that's your in. Recruit a no-bs journalist that wants to hit NK hard, that also has credentials and clear record (no affiliation with any government work), Pyongyang will do their "background-check" eventually, so it makes sense to have a solid cover. Send this person to Hong Kong and have them write for a few months on the political state of China, with a subtle position defending NK's actions and policies. Meanwhile, prep your ground to ground missiles you'll need at least two. The journalist writes for a few months and then requests entry to Pyongyang.

Your journalist is a "marker" or "insider". They're actually harmless and don't need much training. They will be allowed cameras and other various equipment, the objective is to mark spots of value to the dictator. HVT - High Value Targets. So the journalist is given a tour of landmarks and locations of value (memorials/museums/ceremonial locales). They don't have to actually set foot inside or near them, to mark their location and transmit it, they just have to mark three spots NEAR the target and then note which direction and how far from those various points (two will suffice, but three will be more accurate).

Ideally it goes down like this. Two phases, collection and execution. In collection, the journalist marks a few spots of heavy population density, and a time when it is heavily trafficked. He or she also marks other locations of frequent ceremonial importance, this is important later. Phase two, execution... the first missile targets the densely populated location. The timing is key, no one should be there. The objective is to cause worry that these places are vulnerable and cause the dictator to have some kind of ceremonial or overly official public engagement to engage the people. This is where the rub lies. Once he's set a public engagement, you already have the targets lined up and ready to go. Your journalist stays on the ground to verify the kill. Everything goes according to plan (possible), you take him out without causing much collateral damage.

Truth be told, it would never be "easier" to get a shooter/bomber assassin in place to execute some elaborate assassination plot. Their paranoia level has to be used to your advantage. Make them make panic and expose an opportunity to hit them hard. This is the swift version... the slow version is to get a journalist to ally themselves with Pyongyang and fake the funk for a very long time while building an underground network of spies and bombers. Basically what Russia wanted to do to the US in the 50s.

Someone mentioned it already, that faking an antiMuslim message out of Pyongyang would be a pretty elegant solution, but I question whether NK would ever let anyone even remotely Muslim close to their beloved dictator, if such a campaign of misinformation ever started. They're just as capable of protecting their leader from KNOWN threats as any other country, it's the unknown threats they're susceptible to.