/usr/share/fish/completions/atq.fish is in fish-common 2.4.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | #atq
complete -f -c atq -s V --description "Display version and exit"
complete -f -c atq -s q --description "Use specified queue"
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