鈴木さんが知っている。 = Mr.Suzuki knows. (subject→predicate)
It's not anyone else but Mr.Suzuki knows.
鈴木さんは知っている。 = Mr.Suzuki knows.
Mr.Sato doesn't know, but Mr.Suzuki knows.
鈴木さんは知っている。(鈴木さんのことは知っている。) = I know Mr.Suzuki.
I don't know Mr.Tanaka, but I know Mr.Suzuki.
「〇〇は」 makes people pay attention to 〇〇.
It's also very difficult for Japanese to explain about the question.
I hope this will furnish you with some information.