snapshot is a tool that allows developers to snapshot the current state of their device and typically attach its output zip file on the host to issues they file.
snapshot in-tree, you can simply run:
(host)$ fx snapshot
This will output to stdout the path to the generated zip file.
snapshot out-of-tree, you need to SSH into the target and run the target program
snapshot, which will dump the zip file into stdout.
(host)$ <SSH into the target and run `snapshot` on target> > /some/host/path/to/snapshot.zip