Question

What is the action verb in the sentence? the enemy attack the headquarters

Answer 1

The action verb in this sentence is attack because it is what the subject (the enemy) is doing. The action verb will always be what the subject is doing, and is what is affecting the direct object (if there is one).

Answer 2

The answer would be attack, but it should be changed to "attacks" or "attacked" for the sentence to make sense. Hope that helps! :)