Why is tyler durden's last words "What's that smell?"?

Question

From fight club

Answer 1

Rumor has it you can smell the lead and smoke from a bullet when it enters your head.

Answer 2

he smells the gun powder from tyler durden blowing a hole in tyler durden's head.

Answer 3

The narrator shots himself in the head, which blows the back of Tyler's head off (like Tyler stuck a gun in his mouth and shot himself). So there is the smell of gunpower, which happens when you fire a gun. If you look closely the hole at the back of Tyler's head is smoking. That's why he says that. He was probably in disbelief.