You have to scan wilds manually.
The only in-game method to locate wilds is to use the Map view and examine the wildernesses individually to see who the owner is. Many players will capture wilds that are near their cities, which means that you should start looking in the surrounding area. But some players, especially those with more experience, will have wilds that are far from their cities. They do this make it harder to find their wilds. Having to search the entire map to find a person's wilds is a VERY time consuming project.
Therefore, some players choose to use an out-of-game website called Kingdoms of Camelot Tools. (I don't know if outside URLs are allowed here, but do a Google search for koctools, and you should find it.) You can search for a player's or an alliance's cities' locations for free; but to search for a player's wilds, you have to pay a monthly fee of $5 US. (The owner of the site calls it a "donation," but it's really a fee, since you can't use the wilds search if you don't "donate.") The site is useful, but not foolproof. Each server is updated only once or twice a day. So, if a person is trying to hide his or her wildernesses by abandoning their old ones and retaking new ones, then you will not get an accurate report of their wilds' locations unless the site's server has updated the list recently. Some people think it's worth the $5 per month, and others think it's a rip-off. (I am in no way connected with the KoC Tools website, and I am not recommending use of it. I'm just stating what I know about it, and you can decide for yourself about it.)