The correct translation of “میں جانتا تھا کہ وہ وعدہ پورا نہیں کرے گا” is "I knew that he would not keep his promise." This sentence demonstrates the correct sequence of tenses in English when reporting a past belief about a future action. "میں جانتا تھا" translates to "I knew" (past tense). The subordinate clause "کہ وہ وعدہ پورا نہیں کرے گا" expresses a future action from the perspective of the past. In English, when the main clause is in the past tense, the future tense in the subordinate clause typically shifts to the conditional "would."
Therefore, "نہیں کرے گا" (will not do/keep) correctly becomes "would not keep." Option A, "I knew that he won't keep his promise," incorrectly uses "won't" (will not), which is present tense future. Option C, "I was knowing," is grammatically incorrect as "know" is a stative verb not typically used in the continuous form. Option D, "I know he doesn't keep his promise," changes the main verb to present tense and alters the meaning. The chosen option maintains the correct tense sequence and meaning.