my 95 yr old father lives with my husband and myself. he also has dementia and does as you described in asking same thing over and over. i've learned once we've talked about subject few minutes if i either turn my back or have him turn around he forgets what he asked and immediately i can change subject or draw his attention away and into something else. also i've learned never to talk with him while tv volume is on or he is looking elsewhere. when he looks at me he's more likely to retain something. hope this works somewhat for you as well.
my dad is in the early stages of dementia. how do i deal with my frustration when he asks the same questions constantly?