Can you describe some more details about your usecase? 

http://lmgtfy.com/?q=mendix+show+current+user

Create a datasource microflow that returns your current user or current account, add a dataview to your layout and fill it with any information you want to display.

In header i can’t add a data view. 

Below is my home page.

and in header of page there is logout button and we need a user name adjusent to logout button in header to show.