What is the ruling on the wage of an engineer supervising the construction of housing funded by usurious loans, and should he continue in this work?

There is no impediment to accepting supervision of the construction of homes whose owners borrowed their cost from interest-based banks, because your work is not considered assistance in an interest-based loan. The sin falls upon the borrowers, and they must repent. You should forbid them from this evil, for the Prophet, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand; if he is unable, then with his tongue; if he is unable, then with his heart—and that is the weakest of faith."