Anywhere, as long as it avoids damaging major arteries and major organs. Even if a major organ or artery is damaged, if they receive prompt medical attention they can still survive. How much time the person has depends on exactly where they got stabbed. The more important the artery, the quicker they'll bleed to death. Being stabbed in the heart is even worse. Being stabbed in the lungs would result in severe bleeding and a collapsed lung or two (two collapsed lungs = just minutes to live without major medical intervention). Being stabbed in the head will likely result in brain damage and death, however, people have survived and gone on to lead fairly normal lives after things like this.
If you get stabbed in the torso by something blunt, like falling on a metal pole that doesn't have a pointy end, then there's more chance of it passing through the torso between the organs and not actually piercing any organs, leaving to someone surviving an accident that you think they'd have no chance at all of surviving. It's a bizarre phenomenon but has actually happened. Sharp objects however just cut right into organs/arteries, therefore your chances of surviving are much less. The sharper the thing inside you is the more damage it's going to do.
People can survive limbs being amputated if it's done with something that's not that sharp, or through a tearing/searing motion rather than a clean cut. In this circumstance, the muscles of the arterial wall contract and prevent the person bleeding to death. If it's from something sharp like a shark bite or a sharp blade then this doesn't happen and the person bleeds to death. You'd be surprised how much injury humans can potentially survive without medical intervention - although it's dicey as the wrong bacteria getting into what seems to be a fairly minor wound can kill you pretty quickly.
Just to echo what's already been said - a stab wound to the thigh can potentially be fatal pretty quickly if the femoral artery is severed. Medical intervention can prevent death. Similarly, a stab wound to the arm can be fatal if it severs the brachial artery.
The most plausible one for story purposes is a stab wound to the arm, leg, butt or lower abdomen where it misses the artery. Maybe have a doctor comment that it's a good job the stab wound didn't hit the artery or something. If it's the lower abdomen, they'd need medical intervention to repair the damage to the gut or they'll risk a slow and unpleasant death from peritonitis or some other nasty consequence of a damaged gut. Stab wounds to the thorax risk punctured lungs, wounds to the heart or any of the major arteries/veins close to the heart (I haven't mentioned veins but a stab wound to the vena cava (the main vein that goes to the heart) would result in bleeding to death without medical attention) and while most scenarios are those that could still be fixed by a skilled surgeon, if you want the character up and about reasonably quickly I'd stick to the arms, legs or butt, and the knife missing the arteries.
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As long as you miss the femoral artery - it's harder to hit this in the butt, especially if it's a fairly ample butt, than in the thigh.
