Is it permissible to work as a computer trainer inside a public training hall that includes individuals whose identities cannot be controlled or some of whom cannot be prevented, knowing that the training is not on usurious or forbidden programs?

It is forbidden to teach someone that which they will use to commit a sin, whether they are an individual or part of a group. As for the scarcity of job opportunities, it is permissible for one who is in dire need and cannot find a permissible job that fulfills their needs and the needs of their dependents, to work in such a job; due to His (Allah's) saying, exalted be He: "And He has already explained to you what He has forbidden to you, except for that to which you are compelled," and His saying: "But whoever is compelled, neither desiring [it] nor transgressing [its limit] - then there is no sin upon him."