Technically, any Lemmy admin can see every user's upvotes and downvotes — even users on different servers, because that information is federated.

I think there are some sites that expose this publicly as well. So you could probably sort it out.

So I just upvoted you. So an admin can see that but not a mod? Wouldn't an Admin want a mod to suss it out first and just deal with the questionability of it?

Mods don't have access to the backend database, and I don't think Lemmy exposes that information directly by default. It's not a "feature" so much as a natural consequence of the architecture.

Community mods can see votes on posts and comments in their communities.

Lemvotes will show you who's voted, and which way, on any post or comment. By "brigading", are you thinking of activity over more than one post or comment?

Votes are public information thanks to ActivityPub: https://lemvotes.org/ Most frontends (like Lemmy) do not expose this, but the information is out there so any new instance may display counts accurately.

Mods and admins can see who voted what. For mere mortals it's harder, but still possible because it's all public information.

Your lemmy instance will send all of your votes to other instances to be counted (this is not anonymized), so any foreign instance will have your vote history. Sites like lemvotes can then show that to the world.

as has been mentioned lemvotes is the public visible one, but I suspect that most larger admin teams will have access to custom queries from the backend.

I'm learning some deeper SQL for work, so I wrote a back end DB tool as a learning means that can do lots of things like user and instance vote tracking over time:

As a note, lemvotes doesn't always work. There's times it throws errors. But it works most of the time for filthy casuals.

Besides Lemvotes, Mbin instances let anyone see upvotes.