Usually written in kana. Kanji spelling 成すべき
should do; ought to do; must do
Also written なす可き
Expression
誰だれにも成なすべき義務ぎむがある。
We all have a duty to fulfill.
成なすべき仕事しごとを見出みいだした者ものは幸さいわいなるかな。
Blessed is he who has found his work.