Are his keys under the book?一般疑问句就是Are,Is,Do,Does,Will等开头,具体看主语
这里的主语是HIS KEYS,复数,所以将后面的are提前就好
He works in the company.变成Does he work in the company?Work是动词,并且he是单数,所以用does
They work in the company.Do they work in the company?they 是复数
你自己再好好研究一下,很简单的