After 4 month of cardio and using treadmill i feel a small pain in my knee ? shall i stop treadmill ?

Take it easy: you do not have to stop exercising but slow down the intensity like the speed and the inclined if pain persists go to swimming if available until clear by a doctor

Knee pain: I would consider stopping for a few days and then and seeing if an alternate method like cycling or elliptical which has less knee impact causes less pain. Follow up with a doctor /urgent care on your knee as small problems can grow. Consider icing the knee 10 minutes 3 times a day elevating when at rest, and using support like kinesiotape .