Clue: Understand queen's wearing crown lined with fine fabric (9)
Answer: PENETRATE
Explanation: Definition: Understand
 [ ER(abbrev. for "Elizabeth Regina"/Queen Elizabeth) **contained in**(…'s wearing) PATE(crown/one's head) ] **containing**(lined with) NET(fine fabric, consisting of yarn joined together with open spaces inbetween).
Defn: …/to gain insight into something complex or mysterious.