Mrs. Clark, dressed (dress) in a black woolen cardigan, appealed for privacy.

=Mrs. Clark, who was dressed in a black woolen cardigan , appealed for privacy.

解答：以上要填过去分词dressed。dressed in a black wooden cardigan为过去分词短语作(非限制性)定语。
备注：dress 当穿衣为及物动词，即dress sb给某人穿衣服。给某人自己穿衣服dress oneself 被动结构为be dressed, get dressed, be dressed in

She dressed the children in their best clothes.她给孩子们穿上了最漂亮的衣服。

Get up and get dressed !起床穿衣服了！

We must be dressed in uniform at school.  在学校我们必须穿制服.

You should be dressed in black at the funeral.  你在葬礼中该穿黑色衣服.

All the students must be dressed in school uniform on Monday.  星期一所有的学生都必须穿校服.

 She likes to be dressed in red.  她喜欢穿红色衣服.