I do public speaking and debate for a living. One needs to prepare and rehearse short answers that convey the maximum information in the minimum number of words. To do this you need to anticipate what will be asked and have a response ready. Anyone who has ever argued a case in court knows this. Clinton knows this.
The “issues” that Trump will be confronted with are not mysterious - we all know what they are, and how he should respond. He needs to practice those responses.
What are they?