This is a stab in the dark. If you were looking for ST segment elevation, you would want to look at the data provided by the lead over the left ventricle (mid-clavicular line, 5th inter-costal space), which is V4.
Ummm, if you understand that different leads look at different areas of the heart, you will immediately grok the idea that it depends on where the infarct is. For example, inferior/diaphragmatic ischemia is seen best in II, III, and aVF. I will let you go look up what combination of leads show lateral or anterior problems. These are what your faculty wants you to know.