Final answer:
The nurse should instruct Kristin to place the sublingual nitroglycerin tablet under the tongue for rapid absorption during an angina attack.
Step-by-step explanation:
When instructing Kristin on the use of sublingual nitroglycerin (nitro), the nurse should advise that Kristin place the tablet under the tongue. This method allows for the medication to be absorbed directly into the bloodstream through the tissues under the tongue, providing a rapid onset of action which is crucial during an episode of angina (chest pain). It's important not to swallow, chew, or apply the tablet to the skin as these methods would not provide the intended fast-acting relief needed during an angina attack.