We have panelized a PCB and now need to place fiducials on the panel. Is there any idea you can share with us ?

During Panel setup you can create a template that will automatically place panel fiducials, tooling holes, and more.  Go to Panel Setup, and select the tab "Fiducial". Add new fiducials, and make sure to select the layers you wish to add the fiducials.

Here's a tutorial movie showing how to create a complete Panel with Routs, Tabs, Fiducials, Tooling Holes, Rails, and Venting: