How to cast string to boolean in Clojure

You should always think about wrapping code to do this kind of conversion into a clearly-named function. This enables you to be more descriptive in your code, and also allows you to change the implementation if needed at a later date (e.g. if you identify other strings that should also be counted as truthy).

I'd suggest something like:

(defn true-string? [s]
  (= s "true"))

Applying this to your test cases:

(if (true-string? "true")   (println "working") (println "not working"))
=> working

(if (true-string? "false")  (println "working") (println "not working"))
=> not working