Как узнать, какие вопросы задавать во внешнем интерфейсе для системы, основанной на правилах

Это во многом зависит от деталей реализации обратной цепочки. Например, вот как вы можете сделать это в Jess, где движок генерирует цели, которым можно сопоставить правила:

Jess> 
(deftemplate symptom
   (declare (backchain-reactive TRUE))
   (slot name)
   (slot value))
TRUE
Jess>    
(deftemplate diagnosis
   (slot name))
TRUE
Jess>    
(deftemplate question
   (slot name)
   (slot string))
TRUE
Jess>    
(deffacts questions
   (question (name has-fever) (string "Does patient have a fever?"))
   (question (name swollen-neck) (string "Does patient have a swollen neck?"))
   (question (name skin-rash) (string "Does patient have a skin rash?")))
TRUE
Jess>    
(defrule measles
   (symptom (name has-fever) (value yes))
   (symptom (name skin-rash) (value yes))
   =>
   (assert (diagnosis (name measles)))
   (printout t "Patient has measles." crlf))
TRUE
Jess> 
(defrule mumps
   (symptom (name has-fever) (value yes))
   (symptom (name swollen-neck) (value yes))
   =>
   (assert (diagnosis (name mumps)))
   (printout t "Patient has mumps." crlf))
TRUE
Jess>    
(defrule ask-question
   (need-symptom (name ?name))
   (question (name ?name) (string ?string))
   (not (diagnosis))
   =>
   (printout t ?string " ")
   (assert (symptom (name ?name) (value (read)))))
TRUE
Jess> (reset)
TRUE
Jess> (run)
Does patient have a fever? yes
Does patient have a swollen neck? yes
Patient has mumps.
3
Jess> (reset)
TRUE
Jess> (run)
Does patient have a fever? yes
Does patient have a swollen neck? no
Does patient have a skin rash? yes
Patient has measles.
4
Jess>