Husband has mild dementia. Every now and then asks questions and keeps asking even though I answer them. How to respond?

You can answer in a different way.
You in the morning: Honey we are going to the store at 11:00.
Him later: What are we doing?
You: I think we will go to the store today.
Him: Where are we going?
You: Do you want to go to the store? Get your hat, let's go.
Or you can ask him what he would like to do so you turn the question around so he can answer. (keep in mind he may take close to a minute to answer a question.)

I am going to take this a bit further. If you have not yet talked to an Elder Care Attorney you should.
Also if he is a Veteran determine what services he may be eligible for. There are Veterans Assistance Commission offices that will help you get this information and there is no charge for the service.

Agree with PP, BUT before he goes downhill, get all paperwork in order.   DPOA, will, etc.

My advice is to repeat the answer as if he hasn’t asked you before. Think of him as a 3 year old, without a memory. I just answer the same thing over and over again. It can feel frustrating, but I watched my sisters yell at my mom “You don’t remember, Mom!” And I wanted to say to them, “But she doesn’t remember that she doesn’t remember! She can’t help it.” Pray for strength to repeat repeat repeat. There are some good you tube videos you can watch about caring for people with dementia. I o ow it can be overwhelming. I’m sitting under my deck outside right now, taking a break from my 89 year old mominlaw who lives with us. She doesn’t come outside down here, and it gives me a space to relax and and “get away” for a bit.
hugs, and prayers for your strength.