What is the rap Trina and cat sing in car victorious?

You are likely thinking of the song "Make It Shine" from the Nickelodeon series "Victorious". It is not a rap song, but a pop tune that is sung by the entire cast of the show, including the characters of Trina Vega (played by Daniella Monet) and Cat Valentine (played by Ariana Grande).

There are no scenes in "Victorious" where Trina and Cat specifically rap together. They do sing "Make It Shine" with the rest of the cast in several episodes, but it is not a rap song.