My Dad has this recurring event at night that he wants his wife, she is standing right at his side, but insists that it's not her. Advice?

Here are some other threads about the same kind of topic. You'll also probably get some advice about sundowning, since that seems to be what he's doing (having issues in the evening):

https://www.agingcare.com/articles/alzheimers-parent-does-not-recognize-family-144197.htm

https://www.agingcare.com/questions/cope-when-alzheimers-parent-doesnt-remember-family-173959.htm

https://www.agingcare.com/questions/alzheimers-wife-does-not-know-I-am-her-husband-144473.htm

Thank you for your suggestion, I will try this.

A while back, there was a thread where a wife would say, "Oh let me go get her" and leave the room. She'd come back in a few minutes later and say, "I heard you were looking for me?" Then he'd know her. Is there some outfit, or apron, or cologne that your mom could add when she left the room, so that when she came back, he'd have a better chance of "knowing" her because of that piece of clothing or smell? It's worth trying...and heartbreaking at the same time. Hugs to you and your mom and dad...this is so hard on everyone.