Select Effect Titlebar to Display On-screen Controls
When working with an effect in Final Cut Pro, make sure the effect titlebar is selected in the Inspector to display any on-screen controls related to the effect.
With the Playhead parked over the clip, select the clip in the Timeline and open the Video Inspector
Select the specific effect titlebar in the Effects list under the Video Inspector
Final Cut Pro only displays on-screen controls for the currently selected effect. This allows you to apply multiple effects to the same clip, while being able to access on-screen controls for one effect at a time.