I already managed to remove the Dbms Output pane a couple of times from my SQL Developer, probably by doing a keyboard combination by accident.
I am not sure how I did this and I can’t really reproduce this but sometimes I was bugged with this problem.
Problem is that I can’t get this pane back by following the ‘normal’ procedure (going to Menu-> View->Dbms-Output).
Previously I did not found a proper solution for this and I just had to reinstall the sqldeveloper all over again.
Untill now, I found a really easy way to get this pane back.
First of all exit all your sqldevelopers sessions.
Go to the directory where the sqldeveloper is installed (the numbering of the directories could be different from one version to another, but it will look similar to this)
there remove the windowinglayout.xml file
This file contains your ‘custom’ sqldeveloper layout. By removing this the sqldeveloper layout will be reset to the original settings.
Then restart your SqlDeveloper
in sqldeveloper go to Menu -> View -> Dbms_Output
And tadaaa there it is again :)