“Does a nuclear stress test show blocked arteries?”

Nuclear stress testing is one of the modalities to assess for any blocked heart arteries. It can be performed when a patient walks on the treadmill or with the medication, called pharmacological stress test. The Nuclear stress test will not show us the percentage of blockage , but will qualitatively tells us if the area of heart muscle getting reduced blood supply, if it is mildly, moderately or severely reduced. Based on the extent of blockage, we (cardiologists) perform invasive coronary angiography based on symptoms and extent of blockages detected on those imaging techniques.

It shows signs of blocked arteries. It actually does not show the actual artery but if the artery has significant blockage which showed lack of blood flow in that area

Indirectly. By that, I mean the test looks at perfusion to the heart muscles supplied by the various major coronary arteries. So, if a perfusion defect is seen in a specific area of the muscle, there is concern that it’s due to obstructive changes in the artery supplying that territory. If the perfusion defect is "fixed" it likely reflects scarring (typically seen in those who’ve had a prior myocardial infarction). If the defect is "reversible," it means that blood flow to that area of cardiac muscle is compromised when you’re active or when the heart muscle requires more blood supply from an increased need for more oxygen.
I hope this helps!