Final answer:
The verb should be in the past participle form.
Step-by-step explanation:
The verb "eat" in the sentence "Jim Halpert had eat all the sprinkles off his donut by the time I arrived" should be in the past participle form, which is "eaten". The correct sentence should be "Jim Halpert had eaten all the sprinkles off his donut by the time I arrived".
Learn more about Verb tense in English