The figurative language technique employed in the sentence "... or dost thou guess, in the dark?" is a metaphor, as expressed in the first option.
We can eliminate hyperbole, which is the use of exaggeration. Onomatopoeia is the use of words that imitate sounds, so we can also eliminate it. Personification is the attribution of human qualities to inanimate objects, which means it is also incorrect.
We can conclude that the best option is metaphor. The speaker compares guessing to someone who is in the dark, who cannot see.
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