1 (おまえは)大学になんか行けやしないよ。(colloquial, a bit strong words) = You won't be able to go to college. (Because you aren’t so smart or something like that) なんか would emphasize 大学 and (行け)やしないよ is emphasized negative form in colloquial style. 2 おまえだって。(colloquial) = Says you! (You are nothing different from me) When you want to say that it’s not only you, you can use だって. あなただって、あの人だって、先生だって、大人だってetc… 3 行くの行かないのと～ >what is the meaning of と? In this case, you could take it as a abbreviation of とか言いながら or などと言って. 行くの行かないの(とか言いながら)迷ってる。 死ぬの生きるの(などと言って)騒いでる。 4 何が食べたいですか？ = What do you want to eat? 何が食べたいんですか？ = What exactly do you want to eat? >here んcan be replaced by の? Yes. But it sounds a little stiff. 5 行くなら　行くのなら >what is the difference ? It’s the same. >のcan be replaced by ん? Yes. But it would be quite casual. 6 もっと話をしていたい。 = I want to talk more with you. And I hope this situation keeps going. もっと話をしたい。 = I want to talk more with you. 7 取引先に～ > what is に? In this case, it would indicate the place. どこ(に)行くの？ 取引先(に)行きます。