How many people would care about you?这是疑问句.
改成宾语从句应为：
Do you know how many people would care about you?
但最好改成：
How many people do you know would care about you?我们平时说的宾语从句后面应该是陈述句。那how many people would care about you是疑问句为什么又可以作为宾语从句呢？不是要用陈述句吗how many people would care about you? 的确是一个疑问句，但它却也是陈述语序，因为是主语部份带了疑问。宾语从句要用的是陈述语序。