To investigate the SQL code that PL/SQL Developer generates to query the data dictionary views in the database, you can modify the shortcut to PLD by adding the debugsql parameter:
"C:\Program Files\PLSQL Developer 12\plsqldev.exe" debugsql
Then you can investigate the debug.txt file created in the %appdata%\PLSQL Developer 12 directory (e.g. C:\Users\\AppData\Roaming\PLSQL Developer 12)
Remember to remove the debugsql parameter after you are finished investigating, otherwise it can be time consuming for PLD to keep writing the file.
Ask if you have more questions.