Final answer:
The spell that is most similar to Flipendo, the Knockback Jinx, is Stupefy, also known as the Stunning Spell.
Step-by-step explanation:
The spell that is most similar to Flipendo, the Knockback Jinx, is Stupefy, also known as the Stunning Spell. Like Flipendo, Stupefy is used to knock back or stun an opponent. It is a popular offensive spell taught at Hogwarts School of Witchcraft and Wizardry.