Hi CC!
Nigel died in the last episode of season 2 - And the Answer Is...
He was helping Jacen Mazik to blackmail Superman. Yes, he knew that CK = Superman because Jacen had that diary of Tempus and shared the info with Nigel.
At the end of the ep when Jacen thinks they've killed Lois and Superman (and his parents) - Nigel tries to doublecross Jacen and take the diary. But Jacen had toasted to their success and poisoned Nigel's drink (Jacen didn't drink any).
So Nigel died from poisoning at Jacen's hand.
Hope that info helps!
*edit* - oh and his name was Nigel St. John
