Premiere Pro - How to paste effects? (namely opacity)
If you need to copy opacity effect with keyframes, you should select keyframes and press CTRL+C, then select clip on timeline and move playhead to time where you want to put first keyframe, then select effect controls window and click CTRL+V to paste. That's all.

                
            

In such way you can copy keyframes from one clip to another.

If you want to copy keyframes from one clip to a lot of other clips, you can create preset in such way: