Right leg. In ancient China, there was no custom of proposing on one knee. It was introduced to China and became popular in the 18th century. The way of proposing on one knee originated from Western chivalry culture, where Westerners place their left foot in front and right foot behind during duels or archery, and kneel down on their right knee to maintain balance. So when proposing, it is also a gesture of sincerity and politeness to kneel on the right knee.
The method of kneeling on one knee
Stand naturally with your feet shoulder width apart, hands hanging on both sides of your body, take a step forward with your left leg, step forward with your left foot in a bent knee position, kneel on your right leg, and lower your hips. Your left leg should be at a 90 degree angle to your lower leg. Westerners are accustomed to placing their left hand on their chest when proposing to show their devotion.