Best treatment for a sore knee for runner?

These are very different questions, with very different answers (knee soreness vs. knee pain vs. weakened knees to the point they may give out):

Knee soreness is common in runners, and there are many ways to help prevent or lessen this effect:
1. Proper Equipment. For runners, these are primarily running shoes that are specifically made for your foot type, gate, and should be replaced every 400 miles. These shoes should only be used for running, and not as your daily sneaker.
2. Proper Surface/Location. Pavement running can be harder on your knees, and the optimal surface would be a newly-constructed cushioned running track. Trail running can be a good alternative, but could also be more treacherous on knees and ankles, depending on how many obstacles are on the trail.
3. Mileage. Running injuries are caused by going too fast too quick, and too far too soon. It is important to begin with a warm up walk, a run, then a cool down every time you exercise. Equally important is to decide what your running goals are, and if they are distance, to not increase your weekly distance more than 0.5 miles each week during your long-run day.
4. Hydration. Any joint or muscle in your body can feel sore if you are not well-hydrated before, during and after a run (if you are thirsty, you are not drinking enough, even in cold weather!), and it is important to have a well-fueled body, too, with enough food and nutrients to sustain your running.

What are your running goals? How far do you currently run, and how often?

I am assuming that your current health conditions allow you to run safely, and that you do not have any existing conditions with your knees, bones, joints or other soft tissues? Have you been given the "OK" by your doctor to include running as a good form of exercise for you, at this time?

Your other questions regarding knee pain and weak/giving-out knees. These are not the norm for runners, and should be evaluated by your doctor or a specialist. It is important to have all the information before you run, to make sure there is not an underlying condition that is causing the "weak/giving-out" knee, as running could aggravate or worsen this condition.

Please let us know what your doctor says, or if you have any additional questions, as I primarily provided information on how to prevent sore knees...not necessarily how to treat. Do you need more information, and if so, it would be helpful to know more about your current situation (based on the information I provided above).