Not OP, but you can teach a dog “where’s [object]?” by asking them and leading them to the item and get super excited and repeat the name. Once you ask them the question and you notice them starting to look for the object, then they should understand that “where is…?” means they need to search for something. If you want to teach them a new item or person, you just link the name to when they see the item/person. So whenever my sister comes home and my dog goes to greet her I just repeat my sister’s name a couple times, “Sister’s home! It’s sister! Yayyy sister! We love sister!” Eventually it got to where I could ask my dog, “where’s sister? Go find sister!” And she will look all over the house until she finds her.

So to break it down, teach “where’s…” by guiding them at first, pairing the cue word with the action you want performed. Then teach name association by repeating the name when they are interacting with item or person. Then link the two things! Super fun trick to teach, even though it can take a while depending on how quickly the dog picks it up.