I do not understand the abbreviations in City Directories. I know that "r" is resideds, "wid" is widowed, "w" works, "lab" maybe laborer but there are several that I have found that do not make sense to me.
ins
cond
clk
mach
trav
core
collar
supt
I'm sure I can find more. Does anyone know how I can find what the abbreviations mean?

Abbreviations depended on the directory publisher. Most directories I've used have a page for the abbreviations. Go to the very first pages of the directory (before the alpha listing or, if the alpha listings are partway through the directory, start there and scroll a few pages before them). Usually a table of contents will list page numbers for societies, clubs, schools, etc. and abbreviations. (Usually, clk = clerk; cond = conductor; mach = machinist; supt = superintendent. But again, it depends on that book.)

I don't know if you have an Ancestry subscription, so here is an example from a free site that has Chicago directories:
http://chicagoancestors.org/downloads/1900a.pdf
(it takes awhile to load. Scroll down to Image 68 (1 of 29). The abbreviations in this particular directory are at the top of the A surname listings.

Thank you so much!!