At the time of writing the "Contexts View" has a hard-wired blind patch - it doesn't allow you to see a list of actions to which no context has yet been assigned.

Some of these will be in the inbox, but others will scattered amongst all the projects, lurking unnoticed and un-actioned. Users have been reporting losing track of them.

Doubtless Omni will remedy this, but in the meanwhile I have posted a very temporary fix in the Omnifocus Extras forum. It is an applescript which forces actions which lack a context (and which are no longer in the Inbox) to show up in Contexts under an UNASSIGNED heading.

What this lacks (I look forward to a solid Omni remedy), is an ultra-rapid means of then assigning the missing context to such items.

At the moment you have to select such an item, use Apple+Option+R to see it in "Projects View" and then give it a proper context.