doushite watashiga? nande watashiga?

I think it's なぜわたしが？！

なぜ私 ? Naze watashi ?

It depends on the context of your conversation. If someone is looking to blame you for a fault or something: It would probably be enough to just exclaim loudly: DOUSHITE!!? Kung gusto mo malaman ang dahilan kung bakit ikaw (e.g. ang pinili nyang ligawan) tanungin mo ng: DOUSHITE? Understandable na yan sa nihongo.

Trying to guess (ware ga) naze yo? And what i found naze watashi nano?