Final answer:
The quote from 'The Emperor Jones' mainly exemplifies the theme of racism and power, reflecting the protagonist's past and his assertive posture towards racial oppression.
Step-by-step explanation:
The theme most exemplified in the quote from The Emperor Jones is racism and power. This theme is conveyed through the protagonist's implied history with lynching, a form of racial violence, and his defiant attitude toward such experiences. There is also an underlying reference to how power dynamics shift based on context, as Jones threatens to assert his own by possibly killing another person.