I am planning to learn Vue.js , someone told me that I need to learn es6 to continue Vue.js , I asked so many people on this but I need more opinion , I appreciate a lot.
No. Only the browser that run the code cares about what version of JavaScript you use.
ESNext (meaning ES6, ES7, ES8 etc...) will be quite useful indeed.
Like arrows functions, async/await etc... It's not a requirement but it's a nice to have.
Vue.js supports it out of the box too.