Assume I have 2 *.jpg photos of the same location taken from almost the same position.
Unfortunately I edited photo 2 with an editor which does NOT preserve some header information like location.
So this header field is empty/destroyed.
How can I copy location data from photo 1 and save it into the corresponding location header field of photo 2....with ExifTool?
The simplest way would be
exiftool -TagsFromFile Source.jpg -All:All Target.jpg
This will copy all EXIF, IPTC, and XMP data from the source file to the target file. There are some tags that are marked as Unsafe to copy, such as a thumbnail or ICC_Profile, so those won't get copied.
See Copying examples (https://exiftool.org/exiftool_pod.html#COPYING-EXAMPLES) for more commands.