When was the year of Gengshen Tongzhi?

There was no Geng Shennian in Tongzhi period.

There were four Gengshen years in Qing Dynasty, namely:

Nineteenth year of Kangxi 1680

Qianlong five years 1740

Five years of Jiaqing 1800

Xianfeng decade 1860

During the Tongzhi period, there was a Gengwu year, which was 1870.