父はいつも言っている、「最善を尽くせ」と。

、「」。

My father always says, 'Do your best.'

Literal

Father [topic-は] always is-saying, best [object-を] exhaust [quotative-と].

最善を尽くせ uses the imperative form of 尽くす. The quotative と comes after the quoted speech in an inverted structure (quote after the verb). This inverted order places emphasis on the quoted words.