What is the manner of repentance for laughing at a joke that contains mockery of the Prophet Muhammad (peace be upon him), and is it obligatory to declare repentance in front of those present?

A Muslim must denounce any disparagement of the Prophet, peace and blessings be upon him. If unable to do so, he must distance himself from those who mock and denounce it in his heart. Repentance is achieved through regretting what has passed, seeking forgiveness, staying away from the gatherings of such people, and committing to denouncing evil. It is not a condition to declare repentance in front of those who were present.