In short, you should be able to access the directory at /root/sagepipeline_nonomethod/source_dir within your notebook. Explaination follows:
If you open a terminal in the Launcher under Utilities and files, you will arrive at a system terminal. It's the compute environment living in SageMaker Studio, instead of the container where your notebook (kernel) lives.
The /home/sagemaker-user directory is a mountpoint of an EFS, where your Jupyter file browser points to.
sagemaker-user@studio$ df -h
Filesystem         Size  Used Avail Use% Mounted on
overlay             32G  5.3M   32G   1% /
tmpfs               64M     0   64M   0% /dev
tmpfs              1.9G     0  1.9G   0% /sys/fs/cgroup
shm                395M     0  395M   0% /dev/shm
/dev/nvme0n1p1     160G   26G  135G  16% /opt/.sagemakerinternal
127.0.0.1:/200005  8.0E   40M  8.0E   1% /home/sagemaker-user
devtmpfs           1.9G     0  1.9G   0% /dev/tty
tmpfs              1.9G     0  1.9G   0% /proc/acpi
tmpfs              1.9G     0  1.9G   0% /sys/firmware
To access the terminal of the container environment, go to Launcher > Notebooks and compute resources > Open image terminal
The same EFS is mounted on /root
root@datascience-1-0-ml-t3-medium-1abf3407f667f989be9d86559395:~# df -h
Filesystem         Size  Used Avail Use% Mounted on
overlay             32G   40K   32G   1% /
tmpfs               64M     0   64M   0% /dev
tmpfs              1.9G     0  1.9G   0% /sys/fs/cgroup
shm                395M     0  395M   0% /dev/shm
127.0.0.1:/200005  8.0E   40M  8.0E   1% /root
/dev/nvme0n1p1     160G   24G  137G  15% /opt/.sagemakerinternal
devtmpfs           1.9G     0  1.9G   0% /dev/tty
tmpfs              1.9G     0  1.9G   0% /proc/acpi
tmpfs              1.9G     0  1.9G   0% /sys/firmware