How many times did the Prophet Muhammad kiss the Black Stone? And did he kiss it in every round of the circumambulation or only once?

It is sunnah for the circumambulator to kiss the Black Stone in every circuit of the circumambulation if he is able to do so without harming anyone. Otherwise, he should touch it with his hand and then kiss his hand. If even that is not possible, he should point to it. All these actions are recommended and not obligatory, and if he does not perform them, there is no sin upon him.