As has already been mentioned (twice), for KiCad V6 and newer all needed information is inside the schematic (and PCB file for footprints) and this makes it easy enough to move your project to another PC and work on it. But you are likely to get error messages about missing libraries on that other PC.
You also mention you do not know where the library is you created. You can see the full path to a library from: Preferences / Manage Symbol Libraries (Ditto for the footprint libraries). KiCad does not do any searching for library locations, so if you want to use a custom library on two PC's you have to copy the library itself to that other PC, and also add the library to the library table on that other PC. The library tables are in the sym-lib-table and fp-lib-table files. These files can be in your project (for the project specific libraries) or in your configuration directory (for global directories).
On Linux, the configuration directory is in: ~/.config/kicad/9.0 (Where 9.0 is the KiCad version you are using) The configuration directory holds a lot of personalized settings, and you can copy that whole directory to another PC, or use a source code merge program such as meldmerge to transfer only a few settings. If you plan on doing manual edits, I suggest you first make a backup copy of the whole directory. If you make a big mistake, you can also simply delete the whole configuration directory. If you start KiCad and there is no configuration directory for that specific KiCad version, then KiCad assumes it has just been installed, and it creates a configuration directory with defaults.