final particle used express question
欤 is a classical Chinese sentence-final particle that marks a question, similar to a spoken question mark. Its meaning is purely grammatical and does not carry a concrete concept.
欤 is a classical Chinese character composed of 与 (to give, with) and 欠 (lack, yawn). The exact historical development is uncertain, but it likely functioned as a phonetic loan for the question particle.
The left side 与 suggests giving or offering, and the right side 欠 looks like a person with an open mouth. Imagine someone giving a questioning look with an open mouth, as if asking a question.
For ヨ, picture a person asking a question with a rising intonation, like saying 'Yo?' in English. The casual 'Yo?' cues ヨ and fits the questioning function.