Final answer:
The correct verb form to complete the sentence is 'encuentra'.
Step-by-step explanation:
The correct verb form to complete the sentence is 'encuentra'. In the sentence, 'Él hace sus compras por Internet, él encuentra todo lo que necesita en línea', the subject 'él' is singular, so the verb form 'encuentra' agrees with it. The verb 'encuentra' is used in the third person singular form of the present tense. It means 'he finds' or 'he encounters'.
Learn more about Verb form in Spanish