「何が違うの?」は英語で What's the difference? と言います。
この商品とあの商品は何が違うの - What's the difference between this product and that one?
あなたの言ってることと私の言ってること何が違うの?What's the difference between what you said and what I said? もしくは What's the difference between what you're saying and what I'm saying?
Example sentence (例文)
I can't tell the difference between this phone and that one - このスマホとあのスマホの違いが分からない。この tell は「見分ける」と似ています。