How can we tell when my father doesn't remember something or is just not listening?

I'd say it's probably dementia but if he only does this with you then it could be selective hearing or a game. I like the suggestion of mixing it up just to see. If you are going to the clinic, tell him that. The next time he asks, tell him it's the grocery store. The next time tell him it's Chicago. See how he reacts to these things. This could give you a clue whether illness is the reason or if he's playing a game with only you. If so, then you can talk to him about it. If he is developing dementia, then everyone needs to get on board with proper treatment and plans.
Best wishes,
Carol

Memory and hearing issues can be very frustrating. But, you can get used to it and just automatically repeat the answer. With repetition they will get it, sometimes. Sometimes mom will say when will you bring me... when I just gave it to her 5 minutes before. When I reinforced to mom it was okay not to always remember she started feeling safe enough to tell me, I really can't grasp it sometimes, so I need you to repeat it. She will even say, say it again so I can try to understand. Patience and kindness goes very far.

I do not agree with toying with a person who has dementia or hearing loss. For the loved one with dementia, toying with them and telling them you are going to the grocery store instead of the doctor's is just going to confuse them more! And telling them you are going to the grocery store and they are going to the doctor's will make them feel vulnerable, unless you say "We" are going to the doctor. My brother thinks it is very humerous to play with my mother's head. It is cruel, not funny. And when she does get it, she feels very hurt and confused. Why would you want to confuse someone who suffers from confusion through no fault of their own?

I agree with ignoring the nastiness. I have learned that when it gets to over-the-top, I will ask mom directly why are you being nasty to me I am here for you and I love you. Please do not be nasty to me. And she backs off. If she doesn't then I cut the visit short or remain silent and she gets the point. It is negatively reinforcing bad behavior without causing harm. P.S. Mom and I had a horrible relationship throughout life - she was no picnic! But, with time, need and compassion things have so changed! Change is always possible!

He may be hearing you, but his brain does not process the information, so he repeats it back. It is called "echolalia"

Liz, your profile says he has dementia. He really does forget, it is part of the disease. They are often the hardest on the people that do the most for them. If he says he asks where your are going, most likely he really doesn't remember. Hang on, it will get much worse.

Well as an old fart myself, I have selective hearing, I hear what I want to hear. Dementia is not funny, but there are ways to see if he remember, if you are going to the doctor's office and he ask, where are we going? Tell him you are going to the grocery store. If he knows where he is going he'll reply I thought we were going to the doctor. Then you reply; no I am going to the grocery store; you are going to the doctor. Play the same game he's playing. If he truly has the beginning of dementia he will not reply. Just don't say anything if he gets nasty.

If he is playing a game... just tell him You;ll see when we get there, it;s a surprise.. and see if he suddenly "remembers".. And if he is being nasty. just ingnor it.. tell him you;ll speak to him when he remembers his manners. However, if he has dementia.. this many only make him angrier. But my dad hated to be ignored...He would get much nicer if he was not getting attention.

My mom often falls back on the "just joking line" when called on some outrageous comment. I think she can tell - even as out of it as she is - by our faces when shes crossed a line and thats her fall back excuse. Not funny tho, example doc asked her how she got some new bruises (falls) she points to my brother who took her to appt and says he did it. Doc says "what???" she says "I was just playing". Like I said NOT FUNNY.

Pamstegma is correct. Look Echolalia up for yourself.

You can't ever tell unless you ask him. Many times they can't hear so well and just don't ask you to repeat it. Just ask, he will tell you.

You might want to try placing a small object (which is related to the place you are going) in your Father's hand to hold, on the drive there to help him remember. For example, if you are going to the grocery store, perhaps your Dad could hold onto either your real grocery list or a fake grocery list, if you think he may tear it up. When he asks you each time, "Where are we going ?", you can say "Dad, we are going to the grocery store, your are holding the grocery store list, in your hands now. " I am sure, due to his dementia, he will still keep repeating and asking the same question "Where are we going ? " Hopefully, with him holding onto a small object, which is related to each place you visit, it will help him more than current words alone, informing him where you are taking him.
Try and find small items for each place you take your Father, an empty pill bottle could represent either the drug store or doctor's office, etc.
You need to always use the same small object which is associated with each place you take him, in attempt to help him use a combination of a visual object, tactile stimulation = holding the small object in his hand(s), in addition to hearing your answer, every time he asks "Where are we going ? ", all in effort to help his brain with dementia, effected by memory loss.
If you try this and it does not work at first, please don't give up, please keep trying, before you chalk this new method off your list. This method can work, however, it takes time and patience.