Each handler has their own treat. I have seen beef, chicken, hot dogs, liverwurst, cheese. The handler often carries the treat in their mouth.

A lay person can find these treats at the supermarket.

Thank you Jim. I thought the treats were the same and were something special.

We call it "bait" and it can be anything the dog likes. Last night's human's leftover steak or chicken maybe. Lots of handlers use liver, and the show vendors who sell supplies at shows will usually have a cooler of liver to sell, neatly packaged in ziplock baggies. Some dogs prefer toys, even just tiny squeaker toys, altho that can distract the other dogs in the ring and earn the handler dirty looks from others. I've had dogs who would bait for a scrap of kleenex in my pocket.

I just realized that "bait" means many things. It's the treat itself. It's the verb of the handlers act of getting a dog's attention, and it's the dog's reaction behavior, ie, full attention for the judge, as in "my dog would bait for pocket lint" or "my dog only will bait for chicken".

I used to buy liver, dry it in the oven and chop it up.

When I’m in a hurry I buy freeze dried liver online. It is very rich, so I use it sparingly mixed in with their regular kibble. If I put a handful of kibble with a small handful of the dried liver in a ziplock then the smell of the liver rubs off on the kibble.