In Visual Composer 4.8+ the way you enable the Visual Composer for your custom post types is to go to Visual Composer > Role Manager and under the user role you want to set the post types for you click “Custom” from the dropdown then check all the post types you want to use the Visual Composer on.
Old Visual Composer Setup
In version 1.6.3 and greater the Visual Composer should automatically activate for pages, portfolio posts and staff posts. You can easily disable the Visual Composer though for these post types and even enable it for others. This is done via the Visual Composer settings panel as shown in the screenshot below: