How do I get a texbox to display that I can paste a path into for the filepicker?

Hm, I am trying to guess what you are talking about from your very scare information: are you looking for Krunner? That should be accessible with Alt+F2.

Else you need to be slightly more detailed what exactly you are tying to do, with which application. Some more information about your Plasma version and distribution is usually also helpful in this forum...