It is hard work choosing the right words, but we shall be rewarded by the satisfaction that finding them brings.

划线部分为定语从句。

that ：关系代词，先行词是 the satifisfaction

finding：动名词。

finding them： 动名词短语，作定语从句的主语。

brings：定语从句的谓语动词，宾语为关系代词 that。

【翻译】选用恰当的词语虽然很难，不过，如果做到我们则会有满足感。