Good question :)
I’d say all three of them, clearly. But to me the most important one is questioning our approach.
Starting with the fundamentals of our profession. What is a brand? Why are we mistaking it for an artefact, when, in fact, it’s a relationship?
What is our role? What do we help our clients achieve? What value do we, as brand consultants/designers/etc bring to end-users? Then looking at the object of our work: what is identity? How can we understand it better? Where does it live inside an organisation? How is it recognised by end-users? How is it expressed? How does it evolve? How do we reflect that in the way the brand expresses itself?
The relationship with our clients. Where do we fit in in our clients’ organisations and teams? Can we be more than just surrogates? How can our services reflect their needs an their own clients’ needs?
Then there is the content of our work. Strategy. Design.
Then all the long term stuff. Communication. Innovation.
The questions for clients and end-users are important, but approach is fundamental and is what tend to be overlooked more often than not.