Hi,
I would like to suggest few ways to find the list of keyword currently used in your website.
1>Check view source of each page and see what keywords used in meta title, H1 tag & content. These are the very important place where people use keywords to optimize.
2>Second check in webmaster tools & analytics if your site is not brand new. In these two you will find by which keywords website getting traffic.
3>Use open site explorer (a moz tool). To use this tool for keyword ideas, enter website URL and go to the Anchor Text Distribution tab.
I hope above methods helps you.
Thanks