Xcode: View all TODO's in project
You can add a "Run Script" Build Phase to your Target that will look through your entire project for TODO:|FIXME: marks and flag them as warnings.
This new Build Phase will then list all TODO marks as warnings in the Issue Navigator whenever you Build your project %+B.
Here's a link to Ben Dodson's tutorial for doing this with Swift files: https://bendodson.com/weblog/2014/10/02/showing-todo-as-warning-in-swift-xcode-project/
Here is a screenshot of how it looks with a project I've been working on: