Those were the happiest years that Simone had known.
Explanation:
The verb "were" shows that the years that made Simone happy have passed. For this reason, the next verb must also be in the past, so that there is concordance between all the grammar classes present in the sentence. Based on this, the "have known" option should not be used, because it presents the verb tense in the present.
Among the "had known" and "had knew" options, "had known" is used because "know" represents the past participle, which is used with the help of the verb "to have" to express past actions.
