Do you know what your body shape is? The main body shapes are listed here on this fashion blog http://youlookfab.com/2006/04/18/the...-act%E2%80%9D/
For example my main body type is an hour glass shape and my secondary body type is a pear. That means that my hips and thighs will always be wide, they are the first place I gain weight and the last place I lose weight.
What's most important to understand is proportion. It doesn't matter how big your knees are or what your measurements are, as long as you are shaped in good proportion. For example, Beyonce has huge thighs, bigger than you probably see. But she accentuates a tiny waist and has a relatively flat stomach which gives an illusion of being a vixen. So learn what your shape is and how to dress it.
Losing weight on knees is like anything else - lots of cardio and tons of lunges to strengthen the muscles around your knees.