This is the 183rd most frequent Japanese word.
にとって
"にとって" means "for" or "from the perspective of."
In this sentence, 'にとって' specifies the person ('私','me') who considers the books ('これらの本','these books') valuable ('貴重','precious').
これらの本は私にとって非常に貴重です。
These books are very valuable to me.
Here, 'にとって' identifies the individual ('あなた','you') in relation to whom the significance of the experience ('この経験','this experience') is questioned ('どのような意味を持ちますか','what kind of significance does it hold').
あなたにとって、この経験はどのような意味を持ちますか？
What does this experience mean to you?
In this usage, 'にとって' indicates the entity ('地球全体','the entire Earth') for which environmental issues ('環境問題') are considered a serious issue ('重大な課題','major challenge').