Clue: Spot crown jewels kings have left for display (9)
Answer: SPECTACLE
Explanation: Definition: display
Devious: SPEC[k] ('spot' as a noun, a small mark) plus TAC[k]LE ('crown jewels' – more often, and less grandiosely, "the family jewels", I think; anyway, colloquialisms for the male genitalia) minus a K in each particle ('kings having left').