"I ask but he does not answer."

Translation: Tôi hỏi nhưng anh ấy không trả lời.

[Kimm8stuff]

why is there a "dap"

[TehVanarch]

That's a Sino-Vietnamese term.

[Huy_Ngo]

"Đáp" is a short synonym for "trả lời". It appears in many compound words, such as "hỏi đáp" or "vấn đáp" (ask-answer).