The longest days were too short for him, and the shortest nights too long for him.” 3. What is the name for this type of figurative language?
Narrative of the Life of Frederick Douglass

The type of figurative language used in the sentence is: parallelism.

Explanation:

We usually study parallelism as the consistent use of certain structures inside a sentence. But, as a matter of fact, parallelism is also a figurative language. It is still connected to the repetition of grammatical structures, and it usually helps give the idea a certain flow or rhythm.

In the sentence we are analyzing here, the repetition takes place in two clauses. That is, the second cause repeats the structure of the first one, which is something like:

superlative + noun + verb to be + too + adjective + for him

The longest     days        were       too       short         for him

The shortest     nights    (omitted)  too      long          for him

As we can see, the author did not think it necessary to repeat the verb, since it could be easily inferred. But the rest of the structure is exactly the same, creating parallelism.

could you provide an image?