This isn’t a single named effect so much as a compositing technique using layers, masking, and blend modes.

A simple way to build it:

1. Put each person on a separate layer.
2. Remove or isolate the background so the subjects are cleanly cut out.
3. Arrange the layers so one subject is in front.
4. Use a layer mask (alpha channel) on the front subject to hide selected areas and reveal parts of the subject behind.
5. If the look depends on bright areas combining, try blend modes such as Lighten on the top layer.
6. A dark or black background can help, especially with Lighten blending.

So the key terms to look up are layer masks, alpha channels, compositing, and blend modes. In both Photoshop and GIMP, you’ll get the result by combining careful masking with experimentation in layer order and blend mode rather than by applying one canned filter.