I need to call my friend David ____ coat I walked off by mistake yesterday.
I主語,need to call謂語,my friend賓語,David賓語同位語,in whose coat……穿著（某人的）外套…… 做直接賓語；
in whose coat……部分可理解為：I walked off in his coat by mistake yesterday（我昨天穿著他的外套離開的.）
call sb.sth在這里理解為“呼叫（某人）某事,原句可譯為：我打電話告訴我的朋友大衛(wèi),昨天走時(shí)穿錯(cuò)了他的外套.）為什么是 in whose coat所引導(dǎo)的是一個(gè)賓語從句，原句結(jié)構(gòu)是這樣的：I walked off in his coat by mistake yesterday