At which location I have to run ftp client?

Do I have to run ftp client at ~/workspace/ftp_client or
/home/crio-user/ftp_client

you can proceed with ~/workspace/ftp_client

The client can run anywhere. You can change directories (both local and remote) after you login using ftp to the server.
The one thing to note is that the large 1 GB files shouldn’t be under workspace or any sub-directory under workspace.