Very easy on comics, because of the visual element, and also you can sometimes spot an ad next to the main text. Just read a load of comics and use your powers of observation. American examples are the most commercial , usually.
Product placement is when a company pays to have their product appear in a movie or television program. Almost any time you see a real-world brand product in a Hollywood movie today, it is a paid placement. The movie always makes it a point to get at least a short close-up of the product, logo, etc.
I am not aware of such product placements in fiction books.
There are lots of examples of advertiser sponsored comics, and comic books sponsored by other organisations such as religious and anti - left groups, with a specific message to sell, e.g. A particular view on creation (anti Darwin). I'm not sure whether you want this sort of thing for your research, as an extension of product placement. My monograph ' Comics and the World Wars- a cultural recird'(P
I just started reading an e-book called "the disciple of Las Vegas" by Ian Hamilton that I got from out local library after seeing a review in one of our national newspapers. I have lost count of the number of luxury products (clothes, jewellery, food and drink...) mentioned by name in the first 5% of the book. I assume that is all product placement, and it is so irritating that I am probably going to stop reading the book.