noun
nosy person; busybody; insatiably curious person
Describes someone who always wants to know everything about others or about any topic, often to an annoying degree. Can be used lightheartedly or critically.
彼女は本当に知りたがり屋で、いつも人の秘密を聞き出そうとする。
She's a real busybody, always trying to pry out people's secrets.
うちの弟は知りたがり屋で、何でも「なぜ？」と聞いてくる。
My little brother is insatiably curious and asks 'why?' about everything.
Compound of 知りたがり (wanting to know, from 知る 'to know' + たがる 'to want to') and 屋 (suffix for a person with a certain trait).