As your default python version is 2.x , if you don’t have any emphasis on the python 3.x you can try from the first by the below scripts.
pip install --upgrade pip
pip install jupyter
then in jupyter notebook:
!pip install pandas
The version of notebook will be 2.x.
Otherwise install pip3 by the below Linux commands.
sudo apt-get install python3-setuptools
sudo easy_install3 pip
now you can add pandas to the notebook by !pip3 install pandas
.