/usr/share/lightdm/lightdm.conf.d/50-arctica-greeter-guest-wrapper.conf is in arctica-greeter-guest-session 0.99.0.4-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | [Seat:*]
guest-wrapper=/usr/lib/x86_64-linux-gnu/lightdm/lightdm-guest-session
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