his servant waked professor kant and by five, in his slippers, dressing-grown and night-cap, over which he wore his three-comered hat, he seated himself in his study ready for breakfast.

여기서 파란 over which he ~문장이 이해 가지 않습니다. which 가 뭘 말하는건지 독해가 안되요.
도와주세요:)