The easy way- you can view this same thread on kbin, which exposes who is upvoting / downvoting.

The other way-

The way lemmy and the fediverse in general works, anything published on a public instance, becomes public information.

Every action performed, is replicated to every subscribed instance. In this case, I was already working on building a few queries to provide to instance admins to assist with combating spam, and for kicks, I ran a query against some of this thread… and discovered, said user just really likes downvoting my comments.