The student enjoys having English classes.
What is Lily good at?
原因如下：
英语的句子结构是：主语+动词（也就是谓语）+宾语
主语是the students,动词是enjoy having,宾语是English classes.
复数变单数形式时,主语和动词要发生变化：The student enjoys having English classes.（enjoy是主动词才需要变化,但having不用变化,而且enjoy后面的动词一定要加ing.
Lily is good at Chinese.既然是问Lily擅长中文,那么问题就好问Lily好在哪,也就是”什么“,所以应该用”what“.问句就应该是：What is Lily good at?