He works sincerely. The verb in this sentence is a/an-

An intransitive verb is defined as a verb that does not take a direct object.
That means there is no word in the sentence that tells who or what receives the action of the verb.
আলোচ্য বাক্যে কাকে work করেছে বা কী work করেছে প্রশ্নের কোনো উত্তর পাওয়া যায়না। অতএব, ‘work’ এখানে Intransitive verb

Source: dictionary.com