Calling clojure.java.doc.api/javadoc-data-fn returns data about methods of a java class in the :methods and :selected-method entries. It does not include any directly accessible description of the return types for methods. The return type for a method can be found indirectly in the :method-description-html and :method-description-md entries of the :selected-methods (but not the :methods entries).
Example:
(def jdoc-data
(clojure.java.doc.api/javadoc-data-fn "CharSequence/.charAt"
nil))
(def my-method (-> jdoc-data :selected-method first))
> my-method
{:signature "charAt(int index)",
:description "Returns the char value at the specified index.",
:static? false,
:clojure-call "^[int] CharSequence/.charAt",
:method-description-html "<section class ...",
:method-description-md "### charAt {#charAt(int)}\n\nchar charAt (int index)..."}