I made a local copy of my live development environment to test Talend as an ETL tool for Mongodb->Mysql. It's been several years since I last used Talend but everything seems to be generally the same. I followed the instructions from this article https://help.talend.com/pages/viewpage.action?page
Could you please indicate which talend build version you are using? What's Mongo DB version you are using? More information will be helpful for us to address your issue.