How to know whether my PhD advisor knows the area of research?
I suppose it is rather hard to give a satisfying answer to this question with the amount of information available. I mean, it's hard to estimate all the unknowns in this particular case. 


  if yes, then why he did not provide constructive ways to sharp the ideas to get it published in a top conference?


One could speculate in so many different ways; that he does not have the necessary grasp of the field to give meaningful critique is one speculation. Here's another plausible explanation; maybe he wants you to try flying on your own a bit, as a sink-or-swim approach. My supervisor did (and still does) this very often, I have almost too much freedom as to how I write, and what I write and to where I submit, then when the replies and reviews come in we sit down and improve on what I have done. Could be a similar approach

But to come back the question of how to know whether the supervisor is knowledgeable in a particular subject, here are some things that could be useful in the general case:


checking your supervisors publication record. Maybe the s/he has published articles on about this model before you even came to the group. Or maybe he was involved with an older but related model Y?
inquire you supervisor for his interest in the subject. If s/he gives you a paper about model X, all of a sudden then there is certainly a goal with that. To-the-point, effective communication might help you figure out his/her grasp of the field.


EDIT: In reply to the comment: 


  if I have too much freedom as to how I write, and what I write and to where I submit, then whats the point of supervision!


My supervisor often says that his job is to teach me how to do research, not provide me with knowledge or make sure I become successful/famous/rich... Your supervisor has ZERO responsibility in providing you the means to publish in top venues, IMHO. He merely has a responsibility to make sure you get the tools you need to be able to do the research you want to carry out, later on in life. 

As a side comment, I think your perspective to research might cause your frustration with your supervisor. Getting published in top venues is not a birth-right to all hard working grad students; and quite frankly, as a grad student where your articles get published have little to do with you or your work (at least in biomedical research).