/usr/share/X11/locale/ibm-cp1133/Compose is in libx11-data 2:1.6.4-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# ibm-cp1133 Compose Sequence
#
# Sequence Definition
#
#
# This file currently has no entries. It appears that a compose file (even
# just an empty one) is required for the appropriate keysyms to work for
# this encoding.
#
# <Multi_key> Means <Compose>
# Special Character
# End of Sequence Definition
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