非谓语动词he never expected the professor"s lecture was so(boring

oring 作表语修饰lecture,没必要用连接词
句中宾语the professor's lecture was so boring是个省略that的宾语从句
完整句子应该是He never expected that the professor's lecture was so boring.
宾语从句中用陈述语序the professor's lecture was so boring,这是个主系表结构.其中the professor's lecture 做主语,so boring作表语,was是系动词.