If you downloaded the ESP-IDF file using git, you can enter the following command in the "esp-idf" directory...

git describe

Example ( in macOS )

➜  ~ cd esp ↩️
➜  esp cd esp-idf ↩️
➜  esp-idf git:(1329b19fe4) git describe ↩️
v4.4.1

SDK version is showing "v4.4.1".

If you have installed the ESP-IDF tool and set the environment variables, you can use the following command...

idf.py --version

Example 1 ( in macOS )

➜  ~ idf.py --version ↩️
ESP-IDF v4.4.1

Example 2 ( in macOS )

➜  ~ . $HOME/esp/esp-idf/export.sh
.
.
.
Go to the project directory and run:

  idf.py build
➜  ~ idf.py --version ↩️
ESP-IDF v4.4.1

SDK version is showing "ESP-IDF v4.4.1".