There is no way I know of to apply an Effects Mask to more than one clip at a time.
Based on the information of 40 video clips on your Premiere Elements 12 and you wanting to get rid of or obscure a spot on each in about the same location, I have revised my thinking on how to for this one.
I am taking Effects Mask and Adjustment Layer out of the equation and replacing them with a shape created in the Titler/Shapes.
Start with the Timeline Indicator at the first frame of the first video clip.
Create a title in the Titler. The title will go on Video 2. This title will consist of a shape created in the Titler/Shapes to cover just the spot.
a. The shape can be given a color in the Shapes Color Properties dialog to help it blend in. The shape will exist on a transparent background.
b. Once the Titler is closed, the Opacity of the title (shape) can be adjusted. If necessary, a blur applied to the title file.
When all is finished, then just drag the title so that its duration matches the total duration for the 40 video clips.
If you have to edit the shape, double click the title anywhere to open the Titler.
Is that a viable plan for what you would like to do?
I think that this approach is earier than trying to work through Effects Mask and Adjustment Layer in this particular instance.
Add On....There is also the Track Matte approach that I would probably consider before Effects Mask and Adjustment Layer for this.