Are there nonstop flights from Pyongyang (FNJ) to Samjiyŏn (YJS)?

Yes. Air Koryo fly this route. Flight time is about 57m.

Pyongyang → Samjiyŏn

Pyongyang Sunan International Airport (FNJ) to Samjiyŏn Airport (YJS)・378 km

Nonstop flights available (1 airline). Flight time about 57m. Nonstop return flights also operate.

Times are estimated from distance. Check schedules, frequency and availability with the airline or a booking site.