What is the chance to throw a second shuriken with 10 wis, 20 wis, 30 wis and so on ?
It's not clear. Ten Thousand Stars is more like a ranged "doublestrike" chance. Few players take it because high damage with shurikens isn't particularly practical, even if you can throw them slightly faster. Doesn't mean it's not a good consideration with the right (likely crafted) star. I have a lot of Monks but I haven't chosen that enhancement in a long time since there are many other unarmed attack enhancements that are more practical. If I find anything more, I'll reply again.