Hi @DJ Cespedes, You absolutely need to go into the city to talk to them. However, you should ABSOLUTELY not bring address and photos with you as @Account Closed suggested. By bringing addresses and photos into the city you run a very serious risk of turning the owners for a permit/code violation. If you end up doing so, you have materially damaged the sale and the Seller has a serious legal claim against you. Unpermitted ADUs are a really serious issue in Oakland right now and you don't want to get caught up in the middle of it. I had a client who got turned in for this several months ago and it was a huge mess. Your agent should be able to coach you through this conversation.
Generally, you want to ask very, very vague questions like: "If I were to buy a house that has _____ (explain the situation), how could I go about legalizing it? " They will ask for a specific address but you must not give them one.
When you ask City for info, make sure you get the language that defines what an ADU is and is not. That way, you can go back to the structure and look at it for yourself and see if there are any clear/ obvious discrepancies between what is there and what is written. Also, ask the seller for any drawings, plans, or documentation from when they built the unit. As well, you will want to find out if the ADU was built from the ground up or if it was a converted shed/garage. If it is the latter, having the original structure built with permits is important because that can exclude you from the modern setback requirement among others.
If you have more questions, DM me and I'm happy to chat further.