* "Hontou" means "really" or "truly" in English.
* "Konbanwa" is a polite greeting used in the evening, meaning "Good evening."
* "Doku sadai imasuka" is a question, but it's not a direct translation. The closest meaning in English would be "Are you reading?" or "Are you doing any reading?"
Putting it all together, the phrase "Hontou konbanwa doku sadai imasuka" would be a very strange and unnatural sentence in English. It's likely that the Japanese speaker is trying to say something like:
* "Really? Good evening. Are you reading?"
* "Is that true? Good evening. Are you reading anything?"
The speaker is probably expressing surprise or interest in the fact that the other person is reading.