、！！！
H-hey, what are you doing?!
Literal
H-hey! What are-doing [question-か][lengthener-ぁぁ]!!
A stammered scolding, common in manga/anime dialogue. こ、こら is a stammered delivery of こら ('hey!' 'cut it out!' — a sharp rebuke used when catching someone doing something wrong). ナニやっとる is a Kansai-dialect/old-fashioned variant of 何をしている ('what are you doing'): やる instead of する, やっとる as the progressive (a contraction of やっており/やっておる). This dialect/rough form is characteristic of older men, authority figures, or Kansai speakers in fiction. かぁぁ is the elongated exclamation かっ for emphatic delivery. Very vivid, punchy dialogue.