I faced this phrase when the author of the blog post titled The Future Of Lisp wanted to show that nothing is clear: "What, when, why and where did my chicken go?"
What does this phrase mean? Is it an idiom or not?
I think in the context it is being used, "Where did my chicken go?" indicates general confusion - the speaker of this phrase had a chicken and can't find it now. I have never seen this expression before and am basing my interpretation on the context where the writer complains about "a confusing mess", with respect to interoperability between LISP and C/C++ and implies how references to ojects in memory could get lost (much like the chicken) when it is not clear who should should free memory, and when.
It might be that there is an inside joke about "where did my chicken go?" that the author knows, which would make more sense, but I am not aware of it.
I've never heard it, but there is a phrase "a chicken in every pot" to mean a promise by a politician that they will bring prosperity. It's from a 1928 election campaign by US president Hoover
So I suppose "where's my chicken" could mean - where is this prosperity I was promised before the election, although the "chicken in every pot" is not widely used so you would have to be a fairly desperate leader writer to try and coin a new idiom from it.