Ans. A doing word is a word that tells the action of that subject. In terms of parts of speech, the doing word is termed as a verb. We have different kinds of verbs like auxiliary verbs, main verbs, etc. Also, these doing words have different forms in different tenses. Some examples are,
The straw stretched himself from one bank to the other.
The shoe jumped on the straw.
The bubble is watching both of them.
I like swimming.
Sonu goes to school every day.
The highlighted words are nothing but doing words.