There is no single command. However it is good practice to create a requirements.txt file in your venvs anyway. To copy your venv to a new location.
Activate your original venv.
Get your requirements by doing the following in your virtual environment.
pip freeze > requirements.txt
Deactivate your venv.
Then you would want to create a new venv in your desired location. If you are using a specific version of Python, make sure you install it here also.
Copy over the requirements.txt file into the working directory.
Activate your new venv. Then run:
pip install -r requirements.txt
This will install all of the modules (at correct version) from one venv into another.