There's a few examples you could use when surprised, though the emotion they suggest is more confusion than surprise:

{qaStaH nuq jay'} "What the hell is going on?" (from ST6, I think)

{chay'} "What the-?" (from TKD)

(Maybe you could add {jay'} to the previous example to get {chay' jay'} ("What the hell-?"), which has a nice rhyme to it.)