Expresses that something ought to or must be done (equivalent to 'should do'); somewhat formal or literary.
私になすべきことは、まず謝ることだ。
What I ought to do first is apologize.
政府がなすべき対策を速やかに講じる必要がある。
It is necessary for the government to promptly take the measures it should.
彼は自分になすべき責任を最後まで果たした。
He fulfilled the responsibilities he ought to until the end.