Hello, I am new here and have a question... Let's say I have adsense on my www.xyz.com (just an example). How do I know what ads will Google place on my site in terms of the origin of the ads (US ads vs UK ads vs Canada ads). The pay per click for my niche is higher in UK. How should I do to ensure most of the ads are from UK...hehe. Thanks!
The ads are targeted to your content. If a visitor is from the UK, it's more likely to see UK ads because many advertisers use geo targetting.
Write UK targetted content, target UK visitors, use UK web directories, do all you can to get mostly UK.