Jill Biden is very important in managing him. Off the top of my head, there are two events that come to mind where you can clearly see his dementia. One was during the campaign when a BLM protester busted onto the stage and began yelling and jumping around. Jill quickly assessed the situation, knew the protester wasn't posing a threat, and recognized that security would take care of the problem in a few seconds. But you can see the confusion on Joe's face. He wasn't sure what was happening and it took Jill to reassure him that everything was OK. That is a very common scenario with dementia patients.
The other was where he lost his mask last week. He exhibited some irritation (normal) and some degree of panic - and couldn't find it himself. Jill knew it had to be there somewhere and she did a logical and systematic search and found it. I'm sure she is doing a lot of that. If you watch the video of this incident, he couldn't find it after maybe 10 seconds of search, and immediately looked to the staff person behind him and to Jill for help. This is a recognizable part of the disease as well.
Then, in general, we have the cloudy-eyed stare. We also see him getting a question and giving an answer that doesn't really address the question. And we see him searching for words, using the wrong words, mixing up dates, stopping a thought abruptly before he finishes it, and things of that sort. These are all things that go along with dementia.
I saw a clip of him yesterday answering a question about wearing masks indoors with other vaccinated people, he gave an answer, but appeared to sense that it wasn't sufficient, so he told the reporter after a moment of silence that he was just joking - when it clearly wasn't a joke. This was him trying to cover and then he tried to give a better answer, but didn't quite pull it off and it was disjointed and nonsensical.