The definition of cosine-sim in the docs isn't a complete s-exp. Luckily the function is defined in examples.clj:
(defn cosine-sim
[model word1 word2]
(let [rawvecfn #(.getRawVector (.forSearch model) %)
[a1 a2] (map rawvecfn [word1 word2])]
(i-stat/cosine-similarity a1 a2)))