/usr/share/lyx/kbd/american-2.kmap is in lyx-common 2.2.2-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# Contributed by Juergen Vigna (so ask me if you have questions)
# This is a keyboard map for keyboards which do not have dead-keys
# so you can put accents and umlauts on carachters
#
\kmod ' acute aeiouAEIOU
\kmod ` grave aeiouAEIOU
\kmod \" umlaut aeouAEOU
\kxmod acute i í
\kxmod grave i ì
\kxmod acute j ȷ́
\kxmod grave j ȷ̀
# \kxmod acute ' '
# \kxmod grave ` `
# \kxmod umlaut \" \"
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