It varies from person to person, this answer applies to guys too. Some would argue that for a woman it's either the clitoris or g-spot, but for some women that's just not the case. The best way to find out is experimentation, or even just ask her.
Only the woman can answer this, just ask her!! As she would want the most pleasure herself but might be shy to tell you what to do. If you ask the ice is broken!!
There are two types of women. Some women get their orgasm from the clitoris like I do so that's my sensitive spot but the other type of women get their orgasm from the g spot the vagina. Not all women have clitoris