Seiza
Traditional Japanese Sitting
noun, verbal noun
The correct way to sit is this way: traditional Japanese sitting (this is when you sit on your legs and your feet, kneeling). You can also call it seiza. Learning the reading will help with the meaning.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
何でそんなに長い間正座できるの？
How can you sit seiza for that long?
正直、正座は苦手です。
Frankly, I am not good at sitting on my knees.
法要の間ずっと正座をしていたので、足がすごくシビれています。
Since I knelt in seiza throughout the memorial service, my legs have become quite numb.