How do you tell which parts of your novel aren’t working?
The novel isn’t working when it bores me to read it. If pages hold my attention, even after many readings, then the pages work. If they don’t hold my attention, the book has stalled. So then you have to come at things from a different angle. Swing the book around. Find new energy somehow.
The best way to know if what you’ve written has any life is to put it in a drawer and let weeks or months go by. Pull it out again and go over it as a detached reader. Immediately, you’ll see what can be salvaged and what can’t. But few of us have the patience to set our work aside in this way.