The Warring States Policy is an ancient historical document in China, which records many historical events and figures during the Warring States Period (4th century BC to 3rd century BC). As for the Chen Ke you mentioned, he was an adviser of Qi during the Warring States Period. He used to be an official in Chu, and later came to Qi to work for Qi Weiwang.
However, I can't provide detailed information about the specific content of Chen's suggestion when the king of Chu wanted to attack Qin, because his specific suggestion on this matter is not clearly recorded in the existing historical records.
We can learn something about that period through other historical documents. Zuo Zhuan is one of the three biographies of Spring and Autumn Annals, which records some historical events in the Spring and Autumn Period, including the communication between Chu and Qin. For example, in the thirty-ninth year of King Cheng of Chu (633 BC), the King of Chu sent the general Cheng of Chu to lead the allied forces of Chu, Chen, Cai, Zheng and Xu to attack the State of Song, which was an important conflict between Chu and Qin.
In this conflict, Chen Yi may take Chu's side. He knows that Qin is very powerful, so his suggestion may focus on avoiding direct military conflict, but it is more likely to seek diplomatic channels to solve the problem. He may also suggest strengthening the alliance between Chu and other countries to balance the expansion of Qin.
We don't know the specific content of Chen Yi's proposal, but according to the historical background of the Warring States period and his status as a counselor, we can speculate that he may have proposed some diplomatic means, such as marriage and peace talks, to avoid direct conflict. He may suggest that the king of Chu strengthen the alliance with other countries, find the weakness of Qin State, resolve the crisis by diplomatic means, and maximize the interests of Chu State.
This is just a speculation based on the historical environment at that time. The specific situation, due to the lack of historical records, we can't know. If you are interested in more details of this history, I recommend you to read ancient historical documents such as The Warring States Policy and Zuo Zhuan. In addition, there are many historical books and academic studies about the Warring States period, which can also help you understand the situation in that period more deeply.