Fuck knows vulgar slang
A rude or angry way to say that you don't know
Fuck knows who you are! Get out of my way, or else you may regret it.
Fuck knows who stands behind Jack, but I'm going to make him pay the price for insulting me.
Fuck knows where you are gonna take money. You must pay the debt on time.
The origin of this phrase is not clear.
The inexplicable or concealed place or state indicates the afterlife.
I'm very sorry for your dad. He's beyond the veil.