Above command will export your database to dump folder. This folder will be located where you have kept your "data" folder. If you use default "data/db" folder then it will be there but if you use different location then it will be kept over there. This command must be run in normal command prompt, not in mongo shell. It is executable not mongo shell command.   


https://stackoverflow.com/questions/34875913/mongodb-mongodump-is-not-defined