N3
にとって
For, To (from the standpoint of)
タケミにとって一番大切な人は誰ですか?
Takemi, who is the most important person to you?
Explanation
「Nにとって」 means 'for N' or 'to N'. After a person, group, country and so on, it takes that party's point of view and gives a personal judgement: important, necessary, hard, convenient. What follows is usually an evaluation word: 「大切だ」, 「必要だ」, 「難しい」, 「便利だ」. Before a noun: 「にとっての+noun」, as in 「彼にとっての成功」 (success for him).
Mixed up with
「にとって」 is followed by an evaluation (important to him), never by an action or attitude. 「に対して」 is followed by an action or attitude directed at someone: 「先生に対して礼儀正しい」 (polite toward the teacher). 「にとって」 is wrong here.
Before a noun: 「にとっての+N」, 「に対する+N」, 「に関する+N」. These matter a lot in sentence-ordering questions.