whom是宾语,是deal with 的宾语.即deal with whom
"with whom he has dealings"是来修饰everybody的.
举个例子来说明一下吧.把“正在和我吃午饭的这个男人是我的老师”翻译成英语,就是:
The man is my teacher with whom I am having lunch.
英语中一句完整的话就是一个句子,句子末尾必须用逗点.我举的这个例子其实是两句话的组合,即1,The man is my teacher.2,I am having lunch with a man.
这就是英语从句的写法.多读读类似的句子,很自然的就会找到感觉了.