You can cd to YOUR_ENV/lib/pythonxx/site-packages/ and have a look, but is there any convenient ways?
cd
YOUR_ENV/lib/pythonxx/site-packages/
pip freeze list all the
pip freeze
If you are using pip 19.0.3 and python 3.7.4. Then go for pip list command in your virtualenv. It will show all the installed packages with respective versions.
pip 19.0.3
python 3.7.4
pip list