Apart from just searching for the file in the Finder (by hand, like John wrote, or with Spotlight/Sherlock) you could also:
1. Check that your layout is active, then use Ukelele to create a copy with the command 'New from current input source’
2. In Ukelele, open the Organiser and uninstall the keyboard layout by dragging it to the leftmost column.
That will move the file back to where you saved it when you created it.
Actually, this reminds me of a vague wish I’ve had for a long time:
It would be nice if the Organiser would copy a layout file when installing it, as opposed to moving it.
I think this potentially leads to lots of logistic problems, and that’s why I never asked. But now seems to be the moment :-)
When uninstalling a layout, the Organiser would move the file into the trash/wastebasket, unless no file of the same name is found in the target folder.
An alternative would be to move the file back there as currently, but add "uninstalled 2025 01 11" to its file name,