On Sammed Shikhar (Sammed Shikharji / Samet Shikhar), 20 out of the 24 Tirthankaras attained Nirvana (Moksha).

The 4 Tirthankaras who did not attain Nirvana there are:

1. Bhagwan Rishabhdev (Adinath) – Nirvana at Ashtapad
2. Bhagwan Vasupujya – Nirvana at Champapuri
3. Bhagwan Neminath – Nirvana at Girnar
4. Bhagwan Mahavir Swami – Nirvana at Pavapuri

Both Shwetambar and Digambar traditions accept that 20 Tirthankaras attained Nirvana on Sammed Shikhar.

You can read a short description of Sammed Shikharji here and specifically about Sammed Shikhar Parshvanath here