With Trainz PE and the new UI, click the Wrench's icon on the top left menu bar, switch to Surveyor mode, add the train, then switch back to Driver mode
Shortcut Keys;
Ctrl F1 Surveyor Mode
Ctrl F2 Driver Mode
Go to the top drop-down menus and look for the selection with driver mode and surveyor mode in it.
Select surveyor mode to add trains, scenery, etc then select driver mode to continue.