게 죽이다

kill in some manner

죽이다 is the causative of 죽다 — to kill — and the -게 adverb says how it was done: 굉장히 잔인하게 죽였다 'killed very brutally', 혼란하게 죽여버리죠 said of the body destroying faulty cells. 어떻게 죽이지? is simply 'how do I kill it?'. Be careful with the separate slang 죽여주다, which means something is fantastic rather than lethal.