Final answer:
An EMT is most likely to hear wheezes during an asthma attack when the patient is exhaling, due to the obstruction and narrowing of the airways.
Step-by-step explanation:
During an asthma attack, an EMT can expect to hear wheezes most likely while the patient is breathing out, or exhaling. Asthma is characterized by the inflammation and narrowing of the airways, which can result in obstruction during exhalation, causing the characteristic wheezing sound. This difficulty in expelling air is a typical symptom of an asthma attack, indicating that the airways have narrowed and may even be clogged with mucus.