how to open the photoshop ai generative window

Go to Window > Contextual Task Bar

properties -> generative layers icon (should be next to the masking icon)

Check the top panels~ 

After select area -> Edit-> Generative Fill

The small window is not a generative fill window specifically, it’s a general purpose window called the Contextual Task Bar that presents options it thinks are relevant to what’s happening on the canvas. When a selection is active, it offers selection-related options and one of them happens to be generative fill.

If the Contextual Task Bar was accidentally closed and you want to get it back, use the same method you would use to re-open most other windows and panels: look on the Window menu. In this case, choose Window > Contextual Task Bar.

And like c.pfaffenbichler said, it is not the only way to get to generative fill, because even if the Contextual Task Bar is closed, you can also get there by choosing Edit > Generative Fill.

Which exact Photoshop version are you using? 

Is the menu-item Edit > Generative Fill available? 

Now I use the Marquee, the generative fill small window not pop up?..