Which term describes an action of examining for potential issues?

The term that best describes the action of examining for potential issues is "diagnose." In a general sense, to diagnose means to investigate, analyze, or scrutinize a situation, condition, or problem in order to identify any underlying issues or causes. This term is often used in medical contexts to refer to identifying health problems, but it can also apply to various fields, including law enforcement, where officers might assess situations to determine if there are any concerns.

The other terms do not fit this definition as precisely. "Diligent" refers to being careful and persistent in work or effort, but it does not specifically denote the act of examining for problems. "Detain" involves holding or keeping someone in custody, typically related to law enforcement actions rather than examination. "Discreet" indicates a quality of being careful and cautious about what one says or does to avoid causing offense or drawing attention, rather than the action of examining for potential issues. Thus, "diagnose" is the most appropriate term for the described action.