How can I extract a zip code from a location?

Well.. You may have to make some assumptions..... but 

let parts := split(text(Location), " ")

will get you all the parts.  

If we make an assumption that we will address only US Postal Codes.. here is an example.. 

First.. the location of my most favorite place.. 

Parse for US Postal Code

Again.. valid only for US addresses... if you want to use split / parts..