Look Miknik, you need to read it first and understand the passage. Look.
18 The Jews then said to him, “What sign can you show us for doing this?” 19 Jesus answered them, (OK, Jesus is speaking to the Jews here)
“Destroy this temple, and in three days I will raise it up.”
20 The Jews then said, “This temple has been under construction for forty-six years, and will you raise it up in three days?”
The Jews asked for a sign that Jesus is God. Jesus points to the temple and says that if they destroy the temple, he will rebuild it in three days. The Jews think he's mad, because the temple took 46 years to build. Now the recorded conversation is over.
Now John, who was a disciple, adds his comments.
21 But he was speaking of the temple of his body. 22 After he was raised from the dead, his disciples remembered that he had said this; and they believed the scripture and the word that Jesus had spoken.
So what is John saying here? He is saying that when Jesus was resurrected, he came to the disciples, and explained all the scriptures, (the Law, Psalms and Prophets), which prophesied of him, including those which prophesied of his resurrection. So in the course of that explanation, the disciples remembered this particular comment made by Jesus to the Jews.
John tells us that they believed scripture, (i.e. those about his death and resurrection), and they believed this word. Now clearly if the disciples only believed this word after Christ had resurrected, then they did not understand it at the time he made it. This means that the conversation ended where John shows it ended, with the Jews asking how he intended to rebuild the temple in 3 days.It also means that there was no ambiguity when Jesus made the statement; not only the Jews, but the disciples also, understood him to be referring to the Temple.