How does a Muslim convey enjoining good and forbidding evil to all disobedient people in places where evil is widespread, and is he obligated to denounce it publicly, or should he await a suitable opportunity?

Enjoining what is right and forbidding what is wrong is an obligation, and it may be a collective obligation (fard kifayah) or an individual obligation (fard ayn), as stated by An-Nawawi. Publicly denouncing with a loud voice is permissible if no harm is feared and a response is hoped for, but it may not be sufficient and might require individual counseling. The Prophet's guidance (peace be upon him) showed the importance of individual communication after public denunciation. Enjoining is not obligatory when there is despair of a response, but it remains recommended, as mentioned by Ibn Abd al-Salam.