In Jainism, there are 24 Tirthankaras in each half-cycle of time. We are in the current (descending) half-cycle, and the 24th Tirthankar is Mahavira. He is considered the last Tirthankar of this cycle. There will be no new Tirthankar in this half-cycle. A new set of 24 Tirthankaras will arise in the next half-cycle (the ascending half), but their names and details are not given in the present texts. So, there is no “next Tirthankar” to be born now; the next Tirthankar will appear only in the future cycle.

For more on future Tirthankars, you can read: