My wife is a practicing Muslim but she insists that wearing the Hijāb is no requirement of Islam. Is it obligatory for me as the husband to ensure that she wears the Hijāb? Will I be held responsible if my wife does not wear the Hijāb?
A husband has not been given the right to compel his wife to wear the Hijāb (garment that covers the head and chest). If your wife is intellectually convinced that the Hijāb is not required by Islam, the only thing you can and should do is to have a good exchange of views with her regarding her arguments. You should try to state the stance of Islam in a very polite and humble manner and leave her to ponder over it. Also, keep thinking about your own arguments. At times, one tends to be more dogmatic than rational. Keep thinking on how you can improve your presentation.
In principle, you must try to convince and educate your wife in following any directive of Islam. You have not been authorized to use force in such matters. Also, you will not be held responsible for any deed of your wife if you tried your best to stop her from something that was wrong according to your own perception.