how to log inside of response template?

I found a sloppy way of doing it via

$util.validate(false, $record.entity )

This will generate an error in graphql, but it can show what the value was of a variable.

You can also just stash the value and it will show up in the logs, depending on your settings.

$util.qr($ctx.stash.put("debugthis", $record.entity))

Also note that your log level in AppSync must be set to ALL if you want to see this output.