You can duplicate a track loaded on a deck so it plays on the other deck from exactly the same point.

The deck you're playing only plays the selected part (Drums / Vocal / INST), and the other deck mutes the selected part.

For details, refer to the Instruction Manual > [Part names and functions] > [Deck section] > [30 ACTIVE PART DRUMS button], [31 ACTIVE PART VOCAL button], and [32 ACTIVE PART INST button].

You can read the Instruction Manual [here].