"Sudinu sihasan thayu" refers to the event in Jain tradition when a Tirthankara attains the status of a Tirthankara and gives their first sermon from the Simhasan (lion throne) in Samavasaran after attaining Kevalgyan (omniscience).

If you are asking specifically "Sudinu sihasan thayu e kon?" (Who attained the simhasan on the auspicious day?), in Jainism, each Tirthankara, after attaining Kevalgyan, gives their first sermon from the simhasan in Samavasaran. Most commonly, this phrase is used in the context of Lord Mahavira, the 24th Tirthankara, who attained Kevalgyan under the Sal tree and then gave his first sermon from the simhasan in the Samavasaran.

So, the answer is: Bhagwan Mahavir Swami attained Kevalgyan and gave his first sermon from the simhasan in the Samavasaran.