Student or Learner
what is the diffrence between :
- do you know ....
- do you happen to know ....
- do you know .... This is a neutral question. The speaker is not indicating if (s)he thinks the other person does or should know.
- do you happen to know .... The speaker is indicating that (s)he won't be surprised or disappointed if the other person doesn't know. Perhaps by luck or chance the other person does know, but the speaker realizes that there is a good chance that the other person doesn't know.
This question is similar to 'Do you by any chance know.....?' This sentence even more so indicates that the speaker is not expecting the other person to know. In fact, (s)he most likely will be surprised if the other person knows.
"by any chance" is used to inquire if there is 'any possibility'of', in this case, knowing.