Hi!
I'm currently on the DTA programme. It really depends on which cohort you're a part of (energy, social policy, biosciences)?
I was interviewed by my two supervisors, and another non-DTA member of staff from the department. I think the questions asked largely reflect your proposed area of study and supervisor's interests rather than a general framework. Just make sure you're clued up on the topic and your supervisor's research and you should be fine. Good luck!