How do I look up km catalog # 0

[Jenn's coins]

how do I find the KM# the catalog number

[Fenntucky Mike]

Which coin/s?

The KM#'s are found in the standard catalogs, but you can probably find what you're looking for at https://numismaster.com/?id=-10012282&advancedsearch=true&pageno=1 or https://en.numista.com/catalogue/index.php?e=united-states&r=&ct=coin&im1=&im2=&tb=y&tc=y&tn=y&tp=y&tt=y&cat=y&ru=&ca=3&no=&v=&i=&b=&d=&u=&a=&dg=&m=&f=&t=&w=&mt=&g=&se=. I'd go with numista myself. Those are links to the U.S. coin sections, not sure if that's what you're looking for. 

Recently released modern coins may not have KM#'s assigned yet.