To check yourself, stand in front of a mirror with your feet hip-width apart. If your kneecaps are not aligned with the center of your feet and turn inward, you have some degree of knock knee. If they are not aligned with the center of your knee, but turn outward, you may be bow legged.
If you have knock knees or bow legs and do high-impact activities such as running, you might be a good candidate for an orthotic. A visit to orthopedic physician or a physical therapist may help you identify a need for special inserts or a modified exercise program. If you have lower leg pain, you could try cycling or swimming as an alternative form of exercise.