合ってると思うよ！！ちょっとかたい感じだけど。。 I think it's ok. Japanese can understand you but it sounds a littele bit strange.Because we usually skip subject. If you want to say like a japanese I'd recommend next ones. The meaning is same but if I transelate them to English, it is gonna be `What's that`?? これなに？？（very casual) これは何ですか（polite not very polite)

”何だと”　is not correct. 私はこれも何だか知りたいです。

私も。。。No way Jose. Try some of the following.... これも何って教えてくれない？ But I am wild guessing! Haha!