Sam definitely ______ that!

The sentence requires a verb in the present simple tense to express a habitual action or a general truth. The adverb 'definitely' emphasizes certainty. Among the options, 'doesn't do' correctly forms the present simple negative for a third-person singular subject ('Sam'). The other options are grammatically incorrect in this context: 'isn't do' is ungrammatical, 'isn't going to do' implies a future intention, and 'won't do' implies refusal or future prediction, neither of which fits the certainty implied by 'definitely' in this structure. Therefore, the correct completion is 'doesn't do'.

Answer: doesn't do