How to write the calligraphy inscription today, May 2020 17?

First of all, it depends on whether it is brush calligraphy or hard pen calligraphy.

Brush calligraphy. Using the traditional format, the signature can be divided into two parts. Common only the next paragraph, the format is:

Time (usually not Gregorian calendar)+(%location)+author+(respect) book

Such as: "Ding Chun (Xiahuan) worships books in Gufengtang XX".

In traditional calligraphy, dates are marked by years, and months are marked by lunar calendar, not specific to a certain day.

but

Hard-pen calligraphy, if arranged horizontally, can be in a modern format: May 2020 17 XXX book. If it is vertical, it should also be in the traditional format.