Wow, the stats were taken from Fangraphs but okay.
Quick Example.
Adam Dunn on 2008.
164 K on 517 ABs
What's the percent of Ks?
Strikeout Percentage = Strikeouts / Official At Bats
164/517 = 31.7%
And according to Fangraphs his K% for the 2008 season was: 31.7%
Here's some reading that might help: Link
At bat: Batting appearances, not including bases on balls, hit by pitch, sacrifices, interference, or obstruction.
Am I going too fast?