SLR takes pictures of scenes with a big gap between light and dark, such as bright sky and gloomy ground in the evening. Which exposure should be used for photometry?

This is not just a matter of photometry. There is a good tool to deal with this problem in the scenery film called gray gradient mirror GND.

The lens with grey on it gradually becomes transparent, which can darken the sky. According to the ground exposure, both the sky and the ground can be accurately exposed.

Thousands of expensive, cheap green leaves, only a few dozen pieces in the end of the world. Very useful. Many landscape films in my space use this.