What figure of speech is used in "He would look at the ceiling and at the faces before him, as though he had just returned from a dreamy wonderland”?

The key phrase in this sentence is "as though", which functions exactly like "as if" or "like" to introduce a comparison between two different things. He is compared to someone who had just returned from a dreamy wonderland, but he has not literally been to such a place.

This is a simile. A simile is a figure of speech that makes an explicit comparison between two unlike things using comparison words such as "like", "as", "as if", or "as though". Here, the way the character looks at the ceiling and at faces is compared to the dazed, absent-minded manner of someone returning from a fantasy world.

The other figures of speech do not apply here:

• Personification gives human qualities to non-human things. Nothing non-human is being personified.
• Irony involves a contrast between expectation and reality, or saying the opposite of what is meant. There is no such contrast here.
• Metaphor states that one thing is another without using comparison words. Because "as though" is used, this is a simile rather than a metaphor.

The presence of "as though" is the definitive marker that identifies this as a simile.