What is meant by shahadah (witness) especially in the context of Muslim declarartion of faith. This is usually translated as follows: I bear witness that no-one is worthy of worship but Allah, the One alone, without partner, and I bear witness that Muhammad (pbuh) is His servant and Messenger.
I want to understand how a person who has never met Muhammad (pbuh) in person can be a witness to him and his teachings we received through several dozens of generations?
Shahadah is a declaration of one's belief. We declare our belief in that there is no god but Allah and that the Prophet Muhammad, who is a known personality, is the Messenger of Allah. The objection you have raised is applicable to those who bore witness to this fact during the life of the Prophet as well. This I say because nobody observed the fact that the Almighty Allah selected Muhammad as His Messenger and sent him to the people with the message. The claim of the Prophet was based on some arguments and the arguments are still there.