At the tech company, he was the only suit-wearing employee who stood out in the casual office.

suit-wearing 是由名词 suit（西装）和动词 wear（穿着）的现在分词 wearing 组成的复合形容词。suit 指正式的西装套装，wearing 表示"穿着"的状态。suit-wearing 合起来表示"穿着西装的"，用来形容那些在非正式场合仍坚持穿正装的人。