What the fuck? in swedish

¯\(°_o)/¯ how do i said 'what the fuck' in swedish?

my guess is 'vad knullen' but i dunno if that's right

"Vad knullen?"?? I've never understood why the english would try to piece together something alarming with a fuck. What kind of an expression is "What the fuck?"? It's like if the indians would say "What the elephant?" and expect every country to use that exact phrase too.