1) Should terrorists be tried in a regular courtroom if they commit a terrorist attack in the United States? 2) Is it ethical to give the terrorist the death penalty in a state where they don't have the death penalty? 3) Is it ethical for the United States to go into another country and use interrogation tactics considered to be torture on terrorists, such as with the use of simulated drowning, or the raid on Osama bin Laden's compound?

There are differences of opinion on the question of whether terrorists should be tried in civilian courts, whether the act for which the suspected terrorist is being held was committed inside the United States or in a foreign country. In the case of terrorist suspects accused of committing acts of terrorism inside the United States, however, the answer is relatively simpler, although no consensus exists. Most of the debate on this particular issue centers around terrorists captured in foreign countries and either extradited to the United States or, as was the case in the post-9/11 period, subjected to what was called “extraordinary rendition.” The reason terrorists were incarcerated at the military base at Guantanamo Bay, Cuba, was so that the United States Government could interrogate and try, before military tribunals, terrorist suspects captured overseas without having to be constrained by the constitutional protections afforded American citizens. The concern was that, once inside U.S. borders, terrorist suspects would be afforded those same rights, thereby making their conviction more difficult despite the fact that most such individuals were captured on battlefields and were clearly armed combatants.
Most of the above deals with terrorists captured outside of the United States. In the case of those held for acts committed inside the United States, the situation could be considered different. The federal government does, in fact, have a lengthy and successful record of prosecuting terrorism cases, including those associated with the Oklahoma City bombings and the early (1993) terrorist attack on the World Trade Center in New York City. U.S. laws pertaining to acts of violence committed for political purposes are sufficient for today’s purpose. Where weaknesses in some areas of terrorism laws existed prior to the 2001 terrorist attacks, those were addressed in the U.S.A. Patriot Act, especially provisions intended to target the methods terrorist organizations and state supporters of terrorism like Iran use to raise and move the money needed to finance attacks. In addition, the means to incarcerate even the most dangerous convicted terrorists exist within the United States, although the risks to the U.S. public are higher in the unlikely but possible event any convicted terrorists successfully escape from prison.
Even more so than the question of whether terrorists should be tried in civilian courts for acts committed inside the United States, the issue of capital punishment is especially subject to individual opinions. There are plenty of Americans who oppose the death penalty on principle, so would certainly never acquiesce to the use of capital punishment in terrorism cases. That said, there is a list of federal crimes for which capital punishment is authorized, including terrorism. The U.S. Constitution is very clear on the matter of whether state law can prevail over federal law, and the answer is no. Article VI of the Constitution states:

“This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding.”

So, legally, the federal government can put to death someone convicted of an act of terrorism. Federal authority trumps state and local authorities, so if the jury in a federal capital case convicts with the knowledge that the death penalty is an option, the sentence is legal, and considered moral unless one opposes capital punishment in all cases. Then, the question of morality or ethics is left to the individual.
The third question posed—is it ethical for the United States to go into another country and use interrogation tactics unlawful in the United States, such as waterboarding—is more complicated than the other subjects. Both the U.S. and the laws of the foreign nations in question are involved, as well as the extremely murky area of national security law and the myriad interpretations of existing U.S. laws conceptualized by attorneys with the Department of Justice. As has been widely publicized in the years following the 9/11 attacks, key Justice Department lawyers in the Office of Legal Counsel crafted memoranda justifying the use of “enhanced interrogation” tactics like waterboarding and other physical and mental methods used to elicit information. Immediately following the 9/11 attacks, Congress passed and the president signed Public Law 107-40, which authorized the president of the United States to use

all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001.

Since the passage of that law, it has been the subject of endless debate regarding its intended use—in effect, it was not intended for use against Iraq, according to many members of the legislature, only for terrorist organizations like al Qaeda—with many inside and outside of government arguing that the law has been abused by presidents since its passage to pursue military and paramilitary actions against numerous armed adversaries.  In effect, whether it is ethical to use the authorities granted to the president to capture and even execute terrorists and terrorist suspects in foreign nations depends upon one’s perspective. If you are an American determined to kill or capture terrorists abroad, then the use of this law is ethical. If you believe that the intent of the law has been undermined and exploited for nefarious purposes, then such acts are unethical. If you are a foreign national and believe the laws of your nation preclude such U.S. actions, then, again, those actions are unethical and illegal. Certainly, international obligations such as the United Nations Convention Against Torture, and Other Forms of Cruel, Inhuman, or Degrading Treatment would seem to suggest that American actions could be considered unethical. For others, the war against terrorism justifies extreme measures that skirt if not outright violate established legal norms and ethics.
https://deathpenaltyinfo.org/stories/federal-laws-providing-death-penalty

https://www.aclu.org/other/fact-sheet-extraordinary-rendition

https://www.congress.gov/107/plaws/publ40/PLAW-107publ40.pdf