I am working on a windows phone 8 c# application. I have to get long tap events of Forward and Backward buttons that I have placed in the Application bar, but found only Click e
This is not possible. The ApplicationBar API is quite restrictive, which is a deliberate move by Microsoft to ensure consistency. You cannot handle arbitrary events from the ApplicationBar. If you want this kind of behaviour, you will have to build your own UI to support it.
It is worth noting that your users will not expect 'long press' (more commonly referred to as tap-and-hold) behaviour on the app-bar.