The correct answer is: A. Sammed Shikhar.
Sumtinath Tirthankar attained Nirvana at Sammed Shikhar, a mountain in the Indian state of Gujarat. Sammed Shikhar is one of the most important pilgrimage sites for Jains. It is believed that the 20th Tirthankara, Neminath, also attained Nirvana at Sammed Shikhar.
The other options are incorrect. Parsnath is a mountain in the Indian state of Jharkhand. It is the site where the 23rd Tirthankara, Parshvanatha, attained Nirvana. Girnar is a mountain in the Indian state of Gujarat. It is the site where the 24th Tirthankara, Mahavira, attained Nirvana. Pawapur is a town in the Indian state of Uttar Pradesh. It is the site where the 12th Tirthankara, Vasupujya, attained Nirvana.