だから何なの？

so; therefore

what; how many; you-know-what; that; whatsit; what's the expression; what do you call them; what?; hey!

be; is; indicates past or completed action; indicates light imperative

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question