第一个句子主句是A data breach occurs,后面的是时间状语从句,are supposed to是从句的谓语.
2.whom to notify internally and externally和how customers will be alerted and a public relations plan是两个宾语,其实是两个问题变成了陈述句语序,变成了宾语的两个部分,应该是this includes whom and how,to notify internally and externally是用来修饰whom的,customers will be alerted and a public relations plan是修饰how的