Hey @Saurabh_Periwal,
Welcome to the community 
That error would suggest the path is not correct and doesn’t exist within the docker container you are using. Looking at it you are using a Windows path but the container uses a Linux OS, If you map those files as volumes so add…
-v C:\Users\Client\Documents\DockerEnv:/home/node/dockerenv
You can then set your env variables to /home/node/dockerenv/server.crt and /home/node/dockerenv/server.key that shoudl then solve the problem. You could also copy the 2 files into C:\Users\Client\Documents\Docker-PV\n8n and use /home/node/.n8n/server.crt and /home/node/.n8n/server.key