Are you allowed to show your adsense ads on more than one site? If anyone could tell me, I'd be really grateful
It's very easy all what you need to do is to copy the code and place it on the other website. Use the code for all your websites because google knows the account from the code they generate not from the IP address or the domain name good luck
You can have adsense on as many sites as you want. Just make sure they comply with terms. I also suggest you use new ad channel to track what sites make what and how each one is doing.
I want to reiterate the comment made about channels. Set up a custom URL channel for each site where you place your AdSense code. It makes it much easier to track what's making money, and what's not. You can also create multiple channels within the same site, so you can figure out what part of a single site people are clicking on Google ads. In theory, this could help you earn more, but to be honest I'm not exactly sure how. Cool nonetheless!