Have you seen this Q&A? You should upload an image and explain your data a bit more, for example are the tracks:
- Vertices that make up the track regularly sampled distances or do they vary with time?
- Has the data been truncated to some area of interest or do they just randomly start/stop?
- What GIS system and license level are you using?
I would imagine there are several ways of doing this, one method comes to mind is to rasterize the tracks and add the grids together, cells with the highest value are where tracks most agree. I'm sure someone will offer up a better approach?
- Take each gpx track and convert them into a spatial dataset such as a shapefile with each shapefile containing a single polyline.
- Convert this polyline into a raster dataset. The cells that represent the line are given a value of 1 in a background of zeros. Do this for all layers.
- Add the rasters together and the pixels with the highest value are where the tracks most coincide.
This can be done in QGIS but you would need to look into that as I do not use that software. Also you'll need to experiment on cell size, too small and nothing overlaps, too big then all tracks will coincide.