There are two ways by which you can see your output window in toad.
1. In menu bar, select 'VIEW' drop down and then choose 'DBMS Ouput'.
2. Right click on Data grid window --> Desktop Panels will pop up --> choose 'DBMS Output'.
From both you will get your DBMS output window, there will be one button for setting serveroutput on/off. If corlor is red then OFF else ON.
Hope you got what you wanted in this question.