How many molecules NADH are produced in the Krebs Cycle?
This is slightly depending on which reaction you want to include into the cycle. I count four: 


One when Pyruvate is converted to Acetyl-CoA, 
one when Isocitrate is converted to &alpha;-Ketoglutarate, 
one for the reaction of &alpha;-Ketoglutarate to Succinyl-CoA and 
finally one for the reaction of Malate to Oxaloacetate. 


If you see the reaction of Pyruvate as happening outside of the cycle, it's only the later three. 
See this image (from here) for an overview: