What comes after nonillion?

If you mean the -illion after Nonillion, then your answer would be Decillion, coming from the Latin prefix "decem" meaning 10 as it is the 10th -illlion starting from Million.

I know I'm 15 years late, but I cannot let some rando like Wiki User spit lies as foul as "TILLION" in your undeserving face. You're welcome.