Which one is more correct?
a) Thank you for your help Norman.
b) Thank you Norman for your help.
Both are correct, but missing commas. Norman, here, is being used as a appositive phrase and as such can be placed nearly anywhere in the sentence. The connotation/tone changes with placement, so be careful with it.
“Thank you for your help, Norman.”
This places the emphasis on the thanks, and is usually used when you’re talking directly to Norman.
“Thank you, Norman, for your help.”
This places the emphasis on Norman, and is usually used either when you’re calling Norman out of a group, or you want to emphasize sincerity.