Are you still predicting an assassination while he is actually the President? There certainly lot of people who hate Trump outside politics who would have a motive to assassinate him due to political dislike but an inside CIA led coup is less likely as if they didn't do it prior to inauguration I doubt they will do it now unless Trump does something insane in the future.
In any case if the traditional assassination of getting shot aka the JFK route. It may be difficult to have an open casket preserved corpse for display especially if it is a bullet to the head
Although if the CIA did desire to assassinate him, I would think they would try to make it look like death via natural cause/accident to avoid Trump supporter outrage/open rebellion etc. an ambalmed corpse for display may be more feasible
Perhaps injection with lethal dose of insulin to cause death by hypoglycaemia (which a medical autopsy will have difficulty to find a cause) or alternatively give him a lethal dose of potassium to provoke a heart attack would be a hypothetical CIA method of assassination