What is the responsibility of the manager and the site engineer regarding the collapse of the wall that caused the death of a worker after the manager had been warned about a structural defect?

Whoever is negligent or commits an transgression is liable for compensation. If the negligence originates from both of you, then the compensation is shared between you, each according to the tasks under their responsibility. The specifics of this are referred to the judiciary, and the blood money (Diyyah) is incumbent upon the 'Aqilah (male agnates). If there is no negligence or transgression, then there is no liability for compensation, because the hand of a hired person is considered a hand of trust (Yad Amanah).