Question

6.

Answer 1

Let's look at lines 17-19 again:

17. Its letters, although naturally lying
18. Like the knight Pinto-Mendez Ferdinando-
19. Still form a synonym for Truth-Cease trying!
 
The crucial word here is "like" - it means that the letters are "like" - compared to the knight. A direct comparison such as this one is a Simile - this is the correct answer.

A metaphor is similar to a simile in that it treats something as if it was another thing, but it does not include a direct  comparison.