Perched upon a bust of pallas just aboveboard my chamber door. which best interprets the allusion in this passage

Aboveboard ...

An allusion is a reference to another well-known work (story, piece of literature, a novel), object, or a person.

If you look at words in your sentence, what phrase stands out and sounds like a reference to something?

If you're familiar with Greek mythology, or even if you're not, the "Bust of Pallas" should stand out, making it your allusion. The Bust of Pallas refers to Pallas Athena, the Greek Goddess of Wisdom. A bust is simply a type of sculpture showing the head and chest.