First, all of the debates have been poorly designed because all the journalists had decided that there were no major differences among the candidates, and that minor differences were unimportant. Besides which, journalists today have no expertise in anything other than gaffes & gossip.
Ideally, each debate (especially once the numbers had been reduced to three people), would have focused on a different general topic: the economy, foreign policy, domestic policy etc. The questioners would be experts in the particular fields (unknown but widely admired, in their fields, professors--none of the overexposed talking heads). One would be a journalist specializing in the field with access to the Internet to do rapid checks on credibility and honesty in the answers.
Here are some of the topics that have received little or no attention in all of those debates and examples of the kinds of questions I would like to see asked:
1. Signing statements
Both Obama & Clinton support them. Ask their justification. First question to Obama because he apparently taught Constitutional Law. Press the issue. The Constitution gives the President three options (sign, veto, pocket-veto). Signing statements are not mentioned. Demand a constitutional justification. If they say a President has to point out unconstitutional components of a law, point out that determining the constitutionality of a law is the province of the courts. (That's why the questions need to be asked by experts.)
2. Habeas corpus, Guantánamo, rendition, torture.
We now know that torture was discussed and approved at the highest level of our government. Do they believe a President has the right to establish standards for torture? If they don't, have they thought about some way to prevent some future President (including themselves) from taking on such dictatorial powers?
The guidelines were written some fifty years ago and do not take into account either changes in the relative percentage of family budgets spent on food, housing, energy or the different COLs around the country. Has either candidate a plan to develop new and more rational standards?
The tax code gives preferential treatment to unearned income (dividends, capital gains). Interest on savings is taxed at a higher rate than dividends. Why? Wages are taxed at a higher rate. Why? What is the economic justification for this difference? (Prove to me that all capital gains are reinvested in businesses that generate new jobs. If the free market is so good, why do we have to bribe people--capital gains/losses--to participate in it?)
5. Prison reform
We jail a greater percent of our population than any other country. Why? Do you support reform? Be detailed. What kind? Is jail the right place for drug addicts or the mentally ill?
6. Science policy
Will the candidate depoliticize and support science over religion? Climate change & evolution are obvious issues, but there are others.
We rank near the bottom of industrialized countries. Instead of arguing over phonetics, why don't we study the systems in other countries that produce a more highly educated population and adopt similar educational policies? Why do we insist on local funding and local control when we live in a global world? Is it fair or smart to create pockets of millions of children who, because of where they live, will never be able to compete in that world?
8. Foreign policy
What standards will they apply to the people who will represent the United States in foreign countries? Will they be expected to have expertise in the language and the culture?
9. Gays in the military
10. The country's infrastructure
11. The Internet
Here again, the US lags far behind other industrialized countries, even Korea, in terms of broadband access, speed and cost. The free market is clearly not working here. How would they fix it?
On almost all measures, our "best healthcare in the world" produces the worst outcomes among industrialized countries. How will your plans change this?
For Hillary: yes, everybody must buy in if we are to keep costs under control, but how do you design mandates that don't negatively impact the less economically fortunate? After all, many people who don't have insurance don't have it because they can't afford it (they have to pay the rent, the mortgage, buy food, clothes). And a bare-bones policy in their situations may be worse than nothing. This relates back to the question about the definition of poverty.
Since pharmaceutical companies don't want to spend resources on orphan diseases or vaccines, why not set up a non-profit, governmental organization (along the lines of the NIH) whose sole purpose would be the research, development and distribution of drugs for diseases that Big Pharma says it can't afford to invest in? (We should not as taxpayers have to pay huge, multimillion-dollar salaries to CEOs to entice them to do things that are in the public good.)
I could come up with more, but these questions would be a good start.