How to know my DB user? I use the PL-SQL developer tool. I  log in by using Prodcollops as user name to access the database. How can I find out if  my DB user is Prodcollops, too,  or if  it is just a login name?
As  @a_horse_with_no_name stated in a comment, there is a function USER that returns the user of a session, so 

select USER from DUAL


is a way to find out the user of a session.