I cannot complete my graded assignment

I have not taken that course and am not a mentor for TF, but you should be able to debug this. So something is wrong with the pathname that you have constructed there. If you are working on the course website in a Jupyter notebook, click “File → Open” and then click “New → Terminal”. That will give you a new window with a linux shell and you can explore the file system tree that comes with your assignment. E.g. try:

cd /tmp
ls -lR cats-v-dogs

That should give you a picture of the file system. Why is the file name you tried to open not there? Either your code for constructing the path is incorrect or perhaps the file system tree with your assignment is incomplete for some reason. Following the “Get a Clean Copy” procedure documented here will refresh any missing files.