The phrase "One day I am gonna make onions cry" is a playful and humorous way of expressing confidence or determination to become successful, powerful, or skilled at something. It implies that the person speaking is so skilled or influential that even onions, known for making people cry when chopped, will metaphorically cry or be affected by their actions.
The phrase is not meant to be taken literally; rather, it is a figurative expression of ambition and the belief that the speaker will achieve great things in the future. It's often used in a lighthearted manner to show enthusiasm or to jokingly boast about one's abilities or aspirations.